The open circulatory system is found in some animals like insects and molluscs. Here, the heart pumps blood out into a blood vessel which branches and open ms into spaces in the body cavity called haemocoels. The organs and tissues are bathed in blood and exchange materials occurs between the body cells and the blood. Blood in the spaces eventually flow into vessels leading to the heart. Valves in the heart and blood vessels only allow the blood to flow in one direction. In this system, the distribution of blood to the various body parts is poorly controlled.
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