THOMPSON: ANATOMY OF MOSQUITO. 
175 
aspect at the curve at the shoulder of the cardia, upper bend, are 
like those of the epithelium of the hinder end of the esophagus. 
Immediately beyond the “upper bend,” the esophageal type of epi¬ 
thelium is succeeded by the type characteristic of the cardia and 
stomach. For convenience, the point where the change occurs will 
be called the “ break ” in the epithelium. In mature larvae a band 
of narrow columnar cells ( ann ) much like the adjacent cells of the 
reflected face of the valve, but staining more deeply and with more 
vacuolated cytoplasm, is differentiated on the valve side of the 
“break.” This functions in the pupal stage as a regenerative ring. 
Delicate longitudinal fibers pass from the esophagus across to 
the shoulder of the cardia (/?), outside the valve, as is the case 
with several other Dipterous larvae, but the large blood sinus found 
in the larva of Simulium at this point (Miall and Hammond, : 00) 
is poorly represented in Culex and Anopheles. Miall and Ham¬ 
mond also describe the fibers in the larva of Simulium as muscular. 
My sections and dissections of Simulium do not lend themselves to 
this interpretation. The fibers are evidently not muscular in Culex 
and those of Simulium appear to me to be similar connective ele¬ 
ments from the sheath which encloses both esophagus and cardia. 
If the similar fibers in any form prove to be muscular they must not 
be thought of as representing the longitudinalis muscle-coat. For 
in Dicranota (Miall, ’93) which is exceptional in having the longi¬ 
tudinal muscles developed over the shoulder of the cardia, these 
pass beneath the blood sinus. The fibers are in the usual position 
external to the sinus. In Simulium, Miall has observed a distribution 
of the intima wholly like that observed in the fresh gut of Culex. 
The esophageal valve of Anopheles closely resembles the valve of 
Culex, but has a band of longitudinal muscles within the valve 
between the annular muscles and the epithelial cells of the upper 
part of the reflected face. 
The salivary duct of the Culex larva is an extremely thin-walled 
tube which is not differentiated at any point. It is lined with a 
distinct chitinous intima. It forks as the occipital foramen is passed 
and either branch enters a cylindrical gland. These glands taper 
somewhat at their proximal or duct ends. The lumen is ample and 
not infrequently a distension occurs at the distal end of the gland 
which appears in the living larva as a spherical body of high refrac¬ 
tive index. The epithelial cells of the living gland are almost trans- 
