It is amazing to think that almost all life forms require some type of respiratory system which allows them to take in oxygen and give off carbon dioxide. Going back through evolution, one can see an enormous variety of apparatuses which allow organisms to carry out this kind of gas exchange: starfish have pores distributed throughout their skeletons which serve as respiratory organs; the gills of fish and other sea creatures are organs which expose thin-walled capillaries (tiny blood vessels) to the watery environment for gas exchange; earthworms and salamanders use their moist skin surfaces to exchange gases; amphibians use primitive lungs as well as their skin surfaces for gas exchange; birds have a highly complex system of air sacs throughout their bodies which increase their buoyancy in the air, as well as a complicated system whereby the actual beating of their wings while flying is...