Tetrapod probably had a three-chambered heart, as do modern amphibians and reptiles, in which oxygenated blood from the lungs and de-oxygenated blood from the respiring tissues enters by separate atria, and is directed via a spiral valve to the appropriate vessel — aorta for oxygenated blood and pulmonary vein for deoxygenated blood. The spiral valve is essential to keeping the mixing of the two types of blood to a minimum, enabling the animal to have higher metabolic rates, and be more active than otherwise. The difference in density between air and water causes smells (certain chemical compounds detectable by chemoreceptors) to
Blood-vein Blood-vein The blood-vein, ("Timandra comae") is a moth of the family Geometridae. It has a scattered distribution in western and central Europe north of the Alps. In the British Isles the distribution is patchy outside southern England and Wales. In far eastern Europe – east of a line running roughly from Finland through Estonia –, it is replaced by its sister species "Timandra griseata". The species were split in 1931, only to be subsequently re-merged by most authors. But since 1994, new research has come out in favour of treating them as distinct species. The wings are cream coloured with