THOMPSON: ANATOMY OF MOSQUITO. 
197 
region of the hind gut, the ileo-colon. Between the two sets of 
valves the orifices of the five Malpighian tubules are situated. The 
two regions of the hind gut, the ileo-colon and the rectum, are 
distinguished mainly by the greater diameter of the latter and the 
six rectal papillae on its walls. The epithelium is uniformly flat¬ 
tened, the muscles are much like those of the stomach or cardia, and 
the tracheal supply is extensive. A thin chitinous intima lines the 
hind gut, and is differentiated to form a hirsute belt immediately 
behind the valve at the upper end of the ileo-colon. 
The regions to the alimentary canal of the imago and larva are 
noticeably unlike in several points, and the high degree of adapt¬ 
ability of the Dipterous larva generally, has produced within the 
group marked variations in the morphology of the alimentary tracts 
in the young of closely allied genera. Hence in a sense, the mor¬ 
phology of the larval and imaginal gut are separate problems. In 
the larva of Culex or Anopheles the following regions can be distin¬ 
guished : buccal cavity, pharynx, esophagus, cardia, stomach, ileum, 
colon, and rectum. Of these, the pharynx is not well marked off 
from the esophagus below and at the sides, the cardia is more 
distinct from the stomach than in the imago, but clearly a differ¬ 
entiation of its anterior end, and the colon and rectum pass 
gradually into one another. 
The buccal cavity has columnar epithelium and an epipharynx 
is differentiated on its dorsal wall. The epithelium of the pharynx 
is flattened. This region has the heaviest intima of any part of the 
larval gut and is an organ of peculiar shape with an elaborate muscu¬ 
lature. The buccal cavity of the larva corresponds to the posterior 
end of the proboscis canal and the anterior two thirds of the pharynx 
of the imago. The pharynx of the larva forms the posterior third 
of the pharynx of the fly, while the anterior end of the esophagus 
becomes the antlia. The esophagus has flattened epithelium, strong 
circular, and well developed longitudinal muscles. Esophageal 
diverticula are lacking, but the esophageal valve is more highly 
specialized than the corresponding valve of the imago. It is less 
modified, however, than the esophageal valve of the larva of Ano¬ 
pheles, the alimentary canal of which otherwise closely resembles 
that of Culex. The salivary glands of the mosquito wwiggler are 
cylindrical and the salivary duct is undifferentiated throughout its 
length. It opens, freely on a small area of heavy chitin in the 
