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| Introduction |
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| Materials formed in one part of the body have to be taken up to other parts where they are needed or to be got rid of. This is an essential requirement of most animals. This function is performed by the body fluids. |
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| The movement of the body fluids i.e. blood and lymph from one part of the body to the other parts is called circulation. The circulation of blood was first discovered by William Harvey in 1628. |
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| In lower organisms like the one celled protozoans e.g., amoeba and paramecium, the cell is in direct contact with the surrounding water and there is direct exchange of materials between the cell and the water. So there is no need for a circulatory system. In multicellular higher organisms there is no direct supply of the essential materials to all parts of the body and removal of wastes from the body cells. So there is a need for circulatory system. |
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