Correlation of Organs

Correlation of Organs, the close mutual dependence between different systems and structures within the organism. A three- or four-chambered heart is correlated with the development of lungs; animals with an allantois never have gills; the development of a placenta is all but co-extensive with the presence of milk-glands. So among plants parallel venation of the leaves is almost constantly correlated with monocotyledonous structure; and a restriction of the vegetative leaf-organs will show itself in a counterbalancing modification of flowers and fruit. From the time of Aristotle such correlations have been noticed; but it was not till after the work of Cuvier, Geoffroy St-Hilaire, Goethe, and their contemporaries, that the fact was adequately appreciated. It was only then, in other words, that the organism began to be really understood as a unity of mutually dependent parts. The general proposition that all the organs are partners in the general life, that if one member suffer all the members are more or less influenced, is sufficiently self-evident. But beyond this there are the special facts which show that certain organs are knit together by closer physiological bonds than others, that certain structures stand or fall together, that certain characters have a contemporaneous appearance in the historical evolution. The facts are well known; their explanation in many cases is difficult or quite obscure. See EVOLUTION, VARIATION.