The circulation in Leech is Haemocoelic system. There are no true blood vessels. The blood vessels are replaced by channels called Haemocoelic channels or canals, filled with blood like a fluid. The coelomic fluid contains Haemoglobin.
There are four longitudinal channels. One channel lies above (dorsal) to the Alimentary canal, one below (ventral) to the Alimentary canal. The other two channels lie on either (lateral) side of the Alimentary canal, which serves as a heart and have inner valves. All the four channels are connected together posteriorly in the 26th segment. Thus the circulatory system is designed in Leech to compensate the heart structure.
