42 MOSQUITOES OF NORTH AIMEEICA 



" The labium has for function, for the most part, the protection of the iine 

 setse which form the true piercing organ of Culex. In the females of Culex 

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

 has found a place which suits its taste for piercing, it plants its labellge firmly 

 upon the spot, and a moment later the labium flexes backward in its middle, the 

 setae, firmly grouped together, remain straight and enter the skin, wliile 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 set« it probably first withdraws the 

 two barbed maxillas 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 set», perhaps aiding their withdrawal by the muscles of 

 the labium, for, during the process of extracting the setse from the skin, while 

 they are slowly sinking back into the groove upon the upper side of the 

 straightening labium, the mosquito keeps the labellae pressed firmly upon the 

 skin, 



" The mouth-parts of Culex, as above described, are suspended under a 

 clypeus, or epistom, which is figured from the side in fig. 1, c; from above in 

 fig. 2, c; in length-section in fig. 11, c; and in cross-section in fig. 9, c. This 

 clypeus is the hood-shaped forward continuation of the lower part of a A -shaped 

 piece of chitin which forms the framework of what may be termed the ' face ' of 

 Culex; right and left of the upper portion of this framework pass out the an- 

 tennal nerves, the antennas being supported by the framework itself. 



" The pharynx (fig. 11, p), the tubular continuation of the epipharynx above 

 and the hypopharynx below, as it passes backward, beneath the centre of the 

 A-shaped framework, turns somewhat upward, is narrowed to the valve pre- 

 viously described, then widens slightly again, and, as oesophagus (fig. 11, oe) 

 passes through the oesophageal nerve-ring, in which it is supported by three 

 delicate chitinous rods, which lie, one longitudinally on its ventral surface, and 

 two to the right and left on its dorsal surface. Just posterior to the oesophageal 

 nerve-ring, directly above the nerve-commissure which connects the infra- 

 oesophageal ganglion witli the first thoracic ganglion, the oesophagus suddenly 

 expands into an cesophageal pump, or bulb, the longitudinal section of which is 

 shown in fig. 11, &; the cross-section in fig. 10, 6. This bulb, which is the chief 

 sucking organ in the female Culex, and which I have found in no other dipteron, 

 is supported by three longitudinal chitinous rods, which are stouter continua- 

 tions of the three rods supporting the oesophagus through the nerve-ring. These 

 rods (fig. 10, r) have between them chitin-plates (fig. 10, t) which are suspended 

 from the rods by elastic membranes. On the dorsal plate is inserted a double 

 muscle, or a pair of muscles (bm), the origin of which is in the dorsal part of 

 the chitinous shell of the head. Each of the lateral plates has inserted on it a 

 muscle (6m'), the origin of which is in the chitin of the lower lateral regions of 

 the head. The origin of each of these muscles is in the so-called occipital 

 region of the head, that is, behind the eyes. By the simultaneous contraction of 

 these muscles (hm and hm'), the lumen of the oesophageal bulb is enlarged, and 

 the blood flows into the bulb from the pharynx, and, upon their relaxation, the 

 elasticity of the chitinous walls of the bulb, drives the blood, which can not 

 return to the pharynx because of the closing of the valve at v (lag. 11), into the 

 stomach." 



In the male. 



" The mouth-parts of the male of Culex have not been described, as far as I 

 know, with any degree of accuracy, although, since Swammerdamm's time, the 



