MAXILLARY PALPI; LABIUM 41 



the stouter maxillary palpi just before passing under the clypeus, and immedi- 

 ately afterwards they join the labium, and become imbedded, with the man- 

 dibles, in connective tissue. (See fig. 9, mx.) Their continuations in the head 

 are two delicate chitin-supports, each of which ends in a strong muscle ; this 

 muscle, the retractor maxillae (fig. 10, rm), passes backward and downward 

 through the head, beneath the infraoesophageal ganglion, and has its origin in 

 the posterior basal part of the head. The maxillge probably have no protractor 

 muscle, their forward motion being due to the elasticity of the chitin frame-work 

 of the head. The shaft of the maxillas is very transparent, except near the inner 

 side where the chitin-rod runs ; here it is brownish and more opaque. Out from 

 the above-mentioned chitin-rod extends a very delicate feathering, or corruga- 

 tion, of chitin to the edge of the most transparent portion of each maxilla, as 

 seen upon the basal portion of fig. 5, mx. The tip of the maxillae (fig. 5, mx) 

 is very acute, has none of the before-mentioned chitinous corrugations, but, in 

 their place, near the outer edge, is a row of papillae, which have their tips 

 slightly recurved toward the head, and consequently appear serrate. These 

 papillae are upon the upper surface of the maxillae, as can be readily seen, by 

 preparing the mouth-parts by lateral pressure, as in fig. 1. 



" The maxillary palpi (figs. 1, 2, and 9, mp) are four-jointed in some species 

 of Culex, five-jointed in others. At first sight they appear to be three-jointed, 

 but more careful examination serves to show that the apparent basal joint is 

 made up of two joints, and oftentimes to reveal a very short, knob-like joint at 

 the extremity of what appears to be, at first, the apical joint. At their base the 

 maxillary palpi join the maxillas just before the latter pass beneath the clypeus, 

 and, with the maxillae, join the other mouth-parts, as shown, in section, by fig. 9. 



" The function of the maxillae is, probably, to draw the other mouth-parts 

 into the skin, when Culex bites, for if one watches the maxillary palpi of Culex, 

 while the setae are entering the skin, the setae seem to pierce the skin, and enter 

 it with a slow gliding motion, as if drawn from below, instead of pressed from 

 above ; meanwhile, if one observes carefully, with a lens, the maxillary palpi can 

 be seen to be in an alternating motion, as if the maxillae to which they are 

 attached, pressed, first one then the other, into the skin, and then pulled the 

 other parts after them. The muscles, retractores maxillarum, already described, 

 lend weight to this view of the functions of the barbed maxillae. 



" The labium (figs. 1, 2, and 3, /), the largest of the mouth-parts of Culex, 

 and the only one of them, helping form the proboscis, which contains muscles, 

 forms a sheath opening along the upper side, and receiving in its channel the 

 other mouth-parts (excepting the maxillary palpi), as seen in cross-section in 

 fig. 8 ; it tapers from base to tip, is flexible, has a delicately annul ated structure, 

 and is clothed with hair and scales. At its base it unites with the maxillae, man- 

 dibles, and hypopharynx, and continues into the under surface of the head. 

 Throughout its length it contains, on each side, muscles, which have their origin 

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

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

 form appendages, the labellae, which are seen at Ih 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 

 {mx) . Outside the section of each lobe is seen the section of a portion 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. Each of the lobes of 

 the labium, — the labellae, — is provided with an extensor and flexor muscle (fig. 

 7, me, and mf), and is attached to the labium by a true joint. 



