166 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
stomach in either Culex or Anopheles. Sections show only a grad¬ 
ually increasing affinity for haematoxylin on the part of the cells as 
the esophageal valve is approached. In shape and other characters 
the cells resemble those of the stomach generally and there is 
no alteration in the muscle coats. The stomach extends into the 
seventh abdominal segment and is the longest single region of the 
alimentary canal. Its thoracic end is a narrow tube, but the abdomi- 
nal part is wider and capable of great distension. Here is stored 
the meal of blood while it is being digested. The wall of the 
stomach has an epithelium composed of small cubical cells with oval 
nuclei and granular cytoplasm (pi. 14, fig. 21, st ). The free border 
of the cells is more transparent than the remaining area. Probably 
this corresponds to the “striated border” described by Christophers 
(: 01 ) for Anopheles. The margins of the cells make a very sharp 
line in sections, but I did not succeed in demonstrating a cuticle. 
In the freshly removed stomach the nuclei are not visible and the 
cytoplasm appears filled w r ith refringent granules. Over the surface 
delicate circular and longitudinal muscles pass in an irregular net¬ 
work which cuts the surface into more or less rectangular areas. 
The epithelium often protrudes between the muscles forming 
“islands” of one or more cells. The stomach narrows suddenly 
at the posterior end and a low valve is formed. The tracheal sup¬ 
ply is extensive and the interlacing vessels serve to retain the canal 
in position. 
The physiological dissimilarity between the stomachs of Ano¬ 
pheles and Culex in relation to the malarial parasite may possibly 
be accompanied by visible histological differences, although none 
have so far been described. Conclusive proof awaits the elaborate 
process of removing stomachs from mosquitoes of both genera when 
in the same physiological state, and passing them through all the 
reagents simultaneously. I have not been able to obtain a suf¬ 
ficient number of Anopheles to do this. 
The hind gut .— The anterior end of the first region of the hind 
gut, the ileo-colon, is modified to form a low valve adjacent to 
the valve (pi. 14, fig. 21) which terminates the midgut. The Mal¬ 
pighian tubules open into the circular cleft between these two annu¬ 
lar valves. There are five Malpighian tubules, an unusual number 
among the flies. They extend forward for a space parallel to the 
stomach and then recurve, their tips reaching into the last joint of 
