(d) : The circulatory system of insects is open, whereby blood (haemolymph), flows freely through the body cavity (haemocoel). There is a dorsal vessel which is closed at the posterior end of the abdomen, and runs forward along the dorsal midline and opens in the head at the anterior portion (aorta). There are several chambers and openings (ostia), along the dorsal vessel where blood enters it through valves. The blood is then pumped forward to the aorta and into the body cavity.Blood contains: water - about 90%; inorganic ions - dissolved salts of Na,K,Ca Mg; organic molecules - amino acids, sugars for muscle use; blood cells. Haemolymph does not contain an oxygen carrying pigment like Hb, hence, does not assist in respiration.