CSOPHAGEAL DIVERTICULA T7 
“The appendages of the alimentary canal are :— 
“ The Salivary Glands.—The salivary glands consist of six tubular acini lying 
three upon either side. A duct can be seen traversing almost the entire length of 
each acinus. Shortly after leaving the acinus, the three unite to form a single 
duct. Beneath, and in contact with the lower surface of the subcesophageal 
ganglion, the ducts of each side unite to form a common salivary duct which 
passes forwards and enters the chitinous first portion of the alimentary canal 
close to the base of the proboscis. 
“ The Malpighian Tubules.—These are five in number and open into the first 
portion of the hind-gut immediately beyond the pylorus. Their blind ends are 
held in position in the neighborhood of the rectum by tracheal branches. They 
pass forwards in loops above their origin, so that, in transverse section, as many 
as ten may be seen cut across. 
“The Vascular System.—As in most insects where the respiratory system 
ramifies throughout the whole body, the vascular system is not well developed. 
A dorsal vessel or heart and an anterior prolongation of this (aorta) are the only 
closed blood-vessels. Apart from the dorsal vessel the blood circulates in large 
blood spaces, which lie between the lobes of the fat-body and among the muscles 
and viscera. 
“The dorsal vessel passes close beneath the tergal plates throughout the 
abdomen. It is very thin walled, and is not provided with valves. The upper 
portion is attached to the dorsum at intervals by suspensory fibres (muscular), 
so that a festooned appearance is given in longitudinal section. There is, how- 
ever, no true division into compartments. Laterally large cells (pericardial 
cells) are arranged throughout its entire extent, and fibres of a muscular nature 
(alary muscle) pass from the body wall and end in branches in close connexion 
with the dorsal vessel. 
“ At the first abdominal segment the dorsal vessel dips down beneath the 
mesophragma, lying as it does so in direct contact with the cuticle. In the 
thorax it again arches upwards, and lies between the lower portions of the 
antero-posterior wing muscle close above the anterior portion of the mid-gut. 
“ In the anterior third of the thorax it divides into two smaller portions which 
pass outwards, and coming in contact with the salivary ducts enter the neck. 
“ Blood spaces without definite walls occur throughout the body. The thorax 
especially contains large spaces among the muscles, and the complex fat-body 
which lies between and supports the organ is everywhere bathed with blood 
fluid.” 
The diverticula of the cesophagus are of sufficient interest to warrant further 
remarks. There are three of these diverticula, arising near the posterior end of 
the esophagus. Two of them are dorso-lateral and small, the third one is ven- 
tral and very large and extends into the abdomen. Dufour examined these 
organs carefully and speculated regarding their possible function, assuming that 
they were in some way connected with the digestive process. He called the 
smaller pair “ bourses ventriculaires,” the large one “ panse” or paunch. In 
fact this paunch is the so-called “ sucking stomach,” “ food-reservoir ” or crop of 
many other insects. In the mosquito it is, when expanded, globose, ovoid. Du- 
four states that when empty it is folded into plaits. Graber has determined that 
in flies this organ actually serves as a food-reservoir by feeding them with colored 
liquid. Dufour found that when the stomach of the mosquito is distended with 
blood the paunch is filled with a colorless or faintly amber-tinged liquid. He 
