2006 Volume 46 Issue 4 Pages 184-198
In this paper, we propose a series of comparative anatomical and physiological experiments on the respiration of goldfish and larval bullfrogs to teach the evolution of the respiratory systems in vertebrates. The anatomies of the larval bullfrogs in different stages showed that their lungs develop even more in the earlier stages than the metamorphoses, and that the bloodstreams in the capillaries run on the bulla of the lungs. The experiments under anaerobic conditions showed that larval bullfrogs could respire the air by the lungs in anaerobic water where goldfish could hardly respire, and that the frequency of the lung ventilation of larval bullfrogs temporarily increased under anaerobic atmospheric gases while it decreased under aerobic atmospheres. The experiment showed that the oxygen uptake of larval bullfrogs is distributed equally among the skin, the gills and the lungs in their early stage. According to the development of the metamorphic stage of larval bullfrogs, the oxygen uptake increased in ratio with the lungs while it decreased with the gills. The anatomy of the swim bladder of goldfish confirmed that there are no blood vesicles on the bladder, and a fine pneumatic duct connects the bladder and the pharynx. We recommend this series of anatomies and experiments for overcoming the misconceptions about the respiration of tadpoles and teaching students the origin of the lungs of vertebrates and the evolution into the swim bladders of divergent teleost.
