THOMPSON: ANATOMY OF MOSQUITO. 
151 
haps these maxillary muscles counteract the divergent pull of the 
retractors of the maxilla. The retractors of the maxilla were 
described by Annett and Dutton (: 01 ) as “ muscle attaching max¬ 
illary process to occipital region of the skull.” Possibly the double 
retractor is to be seen in Meinert’s “retractor scalpelli” (’81, fig. 15). 
In the same figure the “ protractor scalpelli ” may represent the pro¬ 
tractor of the maxilla. This protractor is described by Annett and 
Dutton and figured in figure 1, plate 18, but is not named. The 
maxillo-labial muscle is described by Annett and Dutton as “muscle 
to base of labium.” It is less readily traced in other studies and 
may be either the “protractor scalpelli” or the “retractor scuti ven- 
traiis” of Meinert (’81, fig. 16), while it is possible that the muscle 
represented in figure 1, plate 8, of Nuttall and Shipley’s account 
under the name “protractor maxilla” represents it. I have not 
found any muscle that will answer to Meinert’s “ retractor scalpelli ” 
as shown in his figure 16. 
The hypopharynx has a central “body,” the mid-dorsal line of 
which is traversed by the salivary gutter, and thin lateral “ wings.” 
The hypopharynx is continuous with the labium at its first appear¬ 
ance in the pupa (Hurst, ’90) and never becomes a separate stylet 
in the male insect, so that the salivary gutter traverses the dorsal 
face of the labium. At the base of the hypopharynx, the salivary 
gutter becomes continuous with the salivary pump, or as it is more 
often termed, the “receptacle of the salivary duct.” This pump 
(pi. 12, fig. 1) consists of a chitin-lined cup, open above and in front 
into the salivary gutter, and closed behind with a plate of thin 
chitin overlaid by a mass of cells. This plate furnishes insertion 
for two muscles and is pierced by the orifice of the salivary duct. 
When the muscles attached to the plate contract, they draw the 
plate back, out of the cup, and saliva can flow in from the salivary 
duct. On their relaxation, the elasticity of the chitin causes the 
plate to re-enter the cup, forcing the contained saliva along the 
salivary gutter into the wound. Nuttall and Shipley (:01-:03) and 
Annett and Dutton (: 01 ) have carefully described the similar pump 
of Anopheles. In A. punctipennis the pump appears to be of the 
same size as that of Culex in specimens of similar length. The 
hypopharynx receives muscle fibers from the mandibular muscles. 
The muscles which operate the salivary pump, the hypopharyngeal 
muscles, will be described in connection with the pharynx. 
