THOMPSON: ANATOMY OF MOSQUITO. 
173 
of flabellal setae remain spread, but sweep downward in a small arc 
with a flickering motion. The mandibles and maxillae are also in 
incessant rapid motion. At intervals the flabellae are depressed and 
presumably any food that may be entangled on their setae is brushed 
off by the maxillae. When the pharynx is filled with food, an ex¬ 
treme contraction occurs, the crests approach very close to one 
another, and the food is forced into the esophagus. The retractor 
muscles of the flabellae do not produce the flickering movements 
just described, being concerned only with depression of the flabellae. 
They remain tense during the gentler movements. The retractors 
of the pharynx and the elevators of the dorsal plate are also passive. 
The motion appears to be caused by a slight to and fro movement 
of the entire pharyngeal and buccal regions, very possibly due to 
activity of the epipharyngeal and lesser lateral muscles and the lat¬ 
eral dilators of the esophagus. The changes in the pharynx itself, 
as shown by the movement of the crests, can be readily interpreted. 
I believe that the retractors of the pharynx and the elevators of the 
dorsal plate remain tense. This would make the elevation of the 
dorsal plate largely the passive result of the divergence of the crests 
as the pharynx walls separate. Probably the cingulum is the most 
important agent in approximating the walls of the pharynx. The 
diagonal muscles may assist and from their crossed position should 
be able to exert considerable leverage. Perhaps they are the chief 
factor in producing the extreme compression observed when the 
animal swallows, for any very marked contraction of the cingulum 
apparently would tend to close the pharyngeo-esophageal opening. 
The head of the Anopheles larva is proportionally much smaller 
than that of Culex and, as Nuttall and Shipley (:0l-:03) have 
pointed out, is rounded. “ In fact the diameter from above down¬ 
wards is very little less than from side to side, except anteriorly, 
where the dorsal surface slopes downward and forward.” This ros¬ 
tral region is narrow and compressed at the sides, and the flabellae 
and palatum are carried well out beyond the apices of the mandibles 
and maxillae. The flabellae are relatively much smaller than in • 
Culex. Hence they recall the flabellae of the larva of Simulium, 
but are not stalked as are the flabellae of this genus. The maxil¬ 
lary palpi of the Anopheles larva are very large and conspicuous. 
Between the maxillae the homologue of the mental sclerite is recog¬ 
nizable, and in sections labial and hypopharyngeal sclerites are found. 
