Double Circulation in the Amphibian Amphiuma tridactylum

Abstract

THE nature of a double circulation (the separation of the pulmonary and systemic circuits) in amphibians is a highly debated subject. Some maintain^1,2 in accordance with the classical theory of Brücke³ that blood is selectively distributed between the carotid, arches, the aortic and the pulmocutaneous arteries. Others reject this hypothesis^4,5 and advocate an entirely random distribution with no selective preference. Still others^6,7 offer support for a compromise and feel that a separate distribution may prevail under certain conditions. Most investigators arrive at their conclusions from various kinds of injection experiments most of which suffer from a lack of quantitation necessary for an exact evaluation of the mixing conditions. The delicate pressure relations within the heart cavities and larger vessels are also prone to be disturbed when applying such procedures. The material used in earlier experiments was very selective. Species of Rana were the case in point while experiments on Urodeles are very scarce.