An abnormality of the venous system of the cat, with some considerations regarding adaptation in teratological development

Abstract

1) A description is given of an abnormal venous system in an adult male cat. The essential feature of the abnormality consisted in the fact that the blood from the posterior portion of the body was returned to the heart through a vessel which in the thorax had the course and anatomical relations normal to the azygos vein. The homologue of the intrathoracic portion of the normal inferior vena cava was a small vessel receiving only the hepatic and phrenic veins. 2) It is pointed out that this venous system, in spite of its abnormality, was functionally perfect, and in so far displayed a high degree of adaptation. It is farther shown that natural selection acting in the traditional manner simply by the elimination of individuals is apparently altogether incapable of explaining the adaptation shown in the development of such teratological specimens. It is suggested that some form of internal selection offers a possible explanation for such cases.