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arise, and then runs posteriorly toward the last segment. The epithelium 
in this part becomes thick again. At the tenth and eleventh segments 
it becomes narrower, and then begins the rectum (Plate LV, 14). The 
rectum has a very thick muscular wall. The chitinous intima is thick. 
As the anal opening is ventral in the twelfth segment, the position of the 
rectum is almost vertical. 
The appendages of the alimentary canal.— The salivary glands are 
large and tubular. Each one has a narrow duct leading to the pharyngeal 
mass, under which the two ducts unite into one. This common duct 
leads forward and opens into the pharynx (Plate LV, 14). 
The four caeca, attached immediately behind the proventriculus. have 
a broad base and each is glandular in appearance (Plate LV, 14). 
The malpighian tubes are very large and often twisted among the 
convolutions of the alimentary canal and the large fat bodies in the 
abdominal region. There are two pairs, and each pair has a common 
root inserted at each side of the end of the mid-intestine. The tubes 
consist of large cells with prominent nuclei (Plate LVI, 26). 
The vascular system.— The dorsal vessel consists of the heart, which 
is posterior, and the aorta, which leads anteriorly from the heart. This 
vessel lies immediately beneath the skin and above the alimentary canal 
and the four large fat bodies. The heart is the swollen and enlarged 
part lying in the last four segments. The anterior end of the dorsal 
aorta is between the cerebral lobes of the brain. The heart has three 
pairs of ostia situated latero-dorsad. They are furnished with valves 
which lead from the body cavity into the heart. Immediately at the 
anterior end of the heart there is another pair of valvular flaps regulating 
the flow of blood into the dorsal aorta. Along the sides of the heart 
and attached to the ventral side of it are three pairs of wings. Each 
wing has its narrow tip connected to the lateral body wall. The 
pericardium, which forms a narrow sheet along each side of the dorsal 
vessel, extends through the entire length of the heart and a part of the 
aorta. The extension can be readily recognized through the large epithelial 
pericardial cells. These cells are arranged one after another at short 
intervals along the dorsal vessel. The muscles in the wall of the dorsal 
vessel are arranged transversely and longitudinally, but chiefly in the 
latter direction in the aorta, and almost exclusively in the heart. At 
the posterior end of the heart extend three more wings, two lateral and 
