(b) : In each of the segments 7,9,12 and 13 is found a pair of large, thick, muscular and rhythmically contractile vertical vessels, called hearts. They pump blood from dorsal to ventral vessel, while flow in opposite direction is prevented by internal valves. Hearts of 7‌th ‌ and 9‌th ‌ segments connect dorsal and ventral vessels only and are called lateral hearts. Those of 12‌th ‌ and 13‌th ‌ segments connect both dorsal and supra-oesophageal vessels with ventral vessel, and are designated as latero-oesophageal hearts.