(4) Hemoglobin is the pigment that gives blood its colour. Take it away, by removing the blood cells, and the resulting plasma is a very pale yellow. Haemoglobin combines with oxygen, enabling blood to carry 70 times more than if the oxygen were simply dissolved. Haemoglobin,contained in the red cells of the blood and constituting the main site of iron in the body,is present in all vertebrate species. In the human adult it is synthesized in the developing red cells in the bone marrow. Many worms have haemoglobin, but others and also most molluscs have different and more primitive oxygen-carrying pigments, which have not survived into higher forms of evolution.