Circulation in earthworm: There is a closed circulatory system in the earthworm. The earthworm has two main dorsal and ventral vessels. At the anterior end of these two vessels, are four pairs of heart. By the pulsation of the heart, the blood flows and circulates in the body through the ventral vessel. After circulation in the body, the blood reaches the heart through dorsal vessel. The rhythmic contraction of heart pumps the blood into ventral vessels. The blood after circulation returns to the heart, by dorsal vessel valves in the heart. Dorsal vessel is like a one-way door, which keeps the blood flowing in the right direction. Earthworm blood contains red, an ionised pigment called haemoglobin, for the transportation of oxygen. Haemoglobin is found in a plasma fluid. Thus, in the earthworm, the transportation of oxygen and mechanism of respiration is less efficient as compared to man.
