Open system of circulation: It is present in lower organisms eg. cockroach. in this system blood flows through open spaces thus blood is in direct contact with tissue fluids. in this system blood pressure is low hence this system is less active than closed system of circulation.
Closed system of circulation: it is present in higher organisms eg.human. in this system blood flows through closed system of blood vessels thus blood is in indirect contact with tissue fluids. in this system blood pressure is high hence this system is more active than open system.