Blood vessels

Open circulatory system: In an open circulatory system the blood is not always in vessels.

Closed circulatory system: In a closed circulatory system the blood always remians in vessels.

Open circulatory systems- insects etc

• Blood fluid circulates through the body cavity- tissues & cells are bathed directly in blood
• Some animals- movement of muscles helps circulate the blood
• In others -Muscular pumping organ pumps blood- long, muscular tube- lies just under dorsal surface
• Blood enters through pores called ostia & blood…