38 MOSQUITOES OF NORTH AMERICA 



(pi, II, %. 1, Ir), an epipharynx (e), a liypopharynx (h), two mandibles (m), 

 and two maxillge (mx), all sheathed, when in repose, in the labium (I), which 

 receives them into a groove on its upper side. Each maxilla has a maxillary 

 palpus (mp) , which lies outside the labium ; the latter has no palpi. The labium 

 and maxillary palpi are covered with hair and scales ; the other mouth-parts are 

 naked, light brown, setif orm, and transparent ; they all originate at the anterior 

 basal portion of the head, and are, with the exception of the maxillary palpi, 

 of about equal length, that is, about three to four times the length of the head. 

 The maxillary palpi, in the females of Culex proper, are about the length of the 

 head. The scaleless mouth-parts are not jointed, and are the ones which pene- 

 trate the skin in biting. The labrum and epipharynx are united in their whole 

 length, forming a piece which is shown in section in fig. 6, d. The other mouth- 

 parts are free to the base. A pumping organ, trianguloid in cross-section (fig. 

 10, &), is formed by a dilation of the oesophagus behind the oesophageal nerve- 

 ring. Each of the above-mentioned parts will be described more in detail later. 

 In comparative size and strength the mouth-parts would be arranged as follows, 

 the largest and stoutest first : labium, labrum-epipharynx (the name by which 

 I designated this compound piece in diptera), hypopharynx, maxillse, and 

 mandibles. 



" The general arrangement of the mouth-parts, relative to each other, is shown 

 best in fig. 8, which is a figure of a cross-section through the middle of the pro- 

 boscis of a female Culex rufus, while in repose, with the setge sheathed in the 

 labium. The labium {I), clothed on the outer side with its scales and hairs, is 

 wrapped nearly around the other mouth-parts. In it lie the two maxillae {mx), 

 partly enclosing the parts above them, and thus helping to bind the parts to- 

 gether; above the maxillae are the two mandibles (m), and immediately above 

 the mandibles, in the median line, is the hypopharynx (/t), with a thickened 

 middle portion. Eesting on the liypopharynx is the labrum-epipharynx ; the 

 epipharynx (e) is omega-form in section, and above it, delicately attached, is 

 the labrum {Ir). The changes in relative position which the mouth-parts of 

 Culex undergo as they approach the head can be best described in the subsequent 

 description, in detail, of each separate part. 



" The labrum-epipharynx (fig. 1, 5, 6, 7-8; Ir and e) of Culex consists of the 

 thin labrum resting upon and fastened to the epipharynx ; it tapers gradually 

 from base to apex. The epipharynx is omega-form in cross-section, being a chan- 

 nel rather than a tube, a tube being formed by the pressing of the hypopharynx 

 upon its under side. The tube thus formed is the channel through which the 

 blood, which Culex sucks, passes into the pharynx. At its base or proximal end 

 the epipharynx is supported and moved by strong muscles having their inser- 

 tions on the upper side of its wings or lateral portions, and upon the upper side 

 of its tube. These muscles extend upward and posteriorly, and have their origin 

 on the inner surface of the clypeus. (See figs. 9 and 11.) These muscles {pm) , 

 by their contraction, elevate, and perhaps slightly retract, the epipharynx and 

 the labrum to which they are attached. These muscles probably aid in suction 

 for when the setaj are all stuck firmly in the skin, the contraction of these muscles 

 would only serve to raise the base of the epipharynx from that of the hypo- 

 pharynx; this action would tend to produce a vacuum between the two (see fig. 

 9), and thus cause the blood to be drawn up in the tube of the epipharynx. The 

 probability that these muscles aid in suction is augmented by the fact, the ex- 

 planation of which I have more fully developed in the part of my dissertation 

 devoted to a comparison of the mouth-parts and suctorial apparatus in the dif- 

 ferent families of diptera upon which I have worked, that the corresponding 

 muscles are devoted to suction in other flies, which cannot raise their epi- 

 pharynx from their other mouth-parts so freely as is seen in fig. 1, and further, 



