How is the circulatory system designed in leech to compensate the heart structure?

Explanation

There are no true blood vessels in leeches. The blood vessels are replaced by canals called haemocoelic canals. These canals are filled with haemocoelic fluid. There are four longitudinal canals. One is dorsal lying above the alimentary canal, another is ventral lying below the alimentary canal. The . remaining two are lateral lying on either side of the alimentary canal. These four canals are connected together at the posterior end. There is no heart, but the lateral channels serve as a heart by being contractile. They have values inside. The dorsal and ventral channels are non-contractile having no muscular walls.