196 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
with all other Hies, the walls and door are rigid and the dorsal roof 
constitutes the plunger of the pump. The pyriform antlia on the 
other hand has walls that are modified to form three racquet¬ 
shaped plates, one dorsal, two ventro-lateral. Tn the narrower 
anterior end of the pump, forward of the circumesophageal nerve¬ 
ring, the walls become unyielding, so that the dorsal plate alone 
retains a limited amount of motion. In correlation with the inac¬ 
tivity of this part of the pump the anterior dorsal dilator muscles 
are vestigial. The Anopheles mosquitoes, which otherwise closely 
resemble the members of the genus Culex in the structure of their 
fore gut, have a more cylindrical antlia, the anterior end of which 
is much less rigid, and the dilator muscles are well developed. A 
valve separates the pharynx from the antlia and a sphincter mus¬ 
cle surrounds the rear of the latter pump as it gives place to the 
esophagus. The esophagus is a thin-walled tube with flattened 
epithelium and poorly developed muscle-coats. The esophageal 
valve is small and immediately in front of it the three esophageal 
diverticula arise. The tracheal supply to the fore gut is scanty, 
but the number of branches which run to the muscles of the 
pharynx and antlia indicate great activity for both pumps. 
Each of the two salivary glands is composed of three acini, the 
middle member being; unlike the lateral in the character of its 
secretions. The ducts from these glands unite in the rear of the 
head and the resulting median duct empties into a cup-shaped 
chitinous pump at the base of the hypopharynx. This pump forces 
the saliva along the salivary gutter of the hypopharynx into the 
wound. 
The two regions into which the midgut may be divided, the 
cardia and the stomach, are not sharply distinguished from each 
other. Their epithelium is low and columnar, the muscle-coats 
are represented by slender longitudinal and circular muscles, and 
caecal pouches are not developed. This last is a point of differ¬ 
ence between Culex and Anopheles, as the latter genus seems to 
possess rudiments of such diverticula. The tracheal supply to both 
cardia and stomach is extensive and the abdominal portion of the 
stomach is capable of great dilatation, serving as a storage place for 
the meal of blood while it is being digested. 
A prominent valve is developed at the posterior end of the 
stomach, opposed to a similar valve at the upper end of the first 
