was imbibed by the paper at the other side. Thus a constant stream of turpentine 

 flowed against the upper side of the mouth-parts, and they were dissolved away, 

 in the field of the microscope, one after the other, in the order, labrum-epi- 

 pharynx, hypopharynx, etc. The position of the parts can be also determined by 

 pressing the head of Cnle.i 1 laterally between a cover-glass and a slide; in 

 perhaps one case out of every twenty tried, the parts will arrange themselves as 

 they did in the specimen from which fig. 1 was drawn. The changes in position 

 which the mouth-parts of Cnh'.r undergo as they approach the head can be best 

 described in the subsequent description, in detail, of each separate part. 



The labrum-epipharynx (figs. 1, 5, 6, 7-8; lr and <?) of Culex consists of the 

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

 from base to apex. The epipharyux is omega-form, being a channel 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 

 Cule.i- sucks, passes into the oesophagus. At its base or proximal end the 

 epipharynx is supported and moved by strong muscles having their insertions 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 fig. 9 and 11.) These muscles (;/<) by 

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

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

 for, when the setae 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 

 hypopharyux; 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 that 

 the corresponding muscles in other flies, which cannot raise their epipharynx so 

 freely from their other mouth-parts as is seen in fig. 1, these muscles are devoted 

 to suction; and further, 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. J 1 , r) 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 during the pumping process. I term the 

 portion in which this sucking process is carried on, the portion of the tube which 

 is between the mouth (where the mouth-parts unite to form a closed tube), and 



