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Acantkia lectularia 
seen to be largely composed of whole blood corpuscles. Considering 
the time that must have elapsed since the previous meal, there would 
seem to be a power of delaying digestion as a defence against prolonged 
.famine. A somewhat similar observed case was one of a flea which 
the writer experimentally fed, giving absolute freedom as regards time. 
After feeding for about ten minutes under a glass, it suddenly shot 
out a speck of black faecal matter which was soon followed by a 
drop of dark red fluid, and then by a drop of what looked like blood. 
Probably the bug in question would have more completely absorbed 
the contents of the rectum if food had been still longer withheld, but 
when a fresh supply became available it made room for it by at once 
clearing out the old store. 
Circulatory System. 
The circulatory system of the bug is of a very simple order even 
amongst insects, where it has been reduced almost to a minimum. 
There is no complex of ramifying vessels to convey the blood, no trace 
even of the diaphragms which in others, such as the bee, divide the 
system into regions and supply motive force to the fluid. There is 
only one vessel, the dorsal aorta, which merges so gradually into the 
heart that it would be difficult to indicate the point of division. On 
opening a bug from the dorsal surface, the almost transparent heart is 
seen lying in the middle line. This organ stretches from the anal end 
right forward to the head, and ends there just behind the brain. It is 
closed posteriorly, and is shghtly pouched on segments five and six. 
These pouches are the heart chambers, and contain the ostia or valves 
on their sides. The organ being very muscular and contracting peri- 
staltically from behind forwards, the blood is driven out at the anterior 
end, and oozing through the spaces between the various organs it 
completes the circuit, ultimately reaching the slight pericardial spaces 
where the cycle is recommenced. Since the blood percolates through 
the interstices between the various organs, the Malpighian tubules are 
thus constantly bathed in the fluid, extracting the waste matter and 
discharging it into the rectum. At the posterior end, and also at the 
level of segment three, there are a couple of thin strands of muscle 
fibres. These moor the heart, and would seem to be the remnants of 
the diaphragms found in insects. There is a slight taper from the 
posterior to the anterior end of the heart, and throughout its length it 
is closely surrounded with cells. In segment three, there is rather a 
