THE AXIAL GRADIENTS IN HYDROZOA

Abstract

Hydroids and hydromedusæ placed in dilute solutions of potassium permanganate show characteristic axial gradients in rate and total amount of reduction of permanganate, as indicated by the coloration of the protoplasm by MnO2 or other products of the reaction. These gradients correspond with the physiological gradients indicated by other methods and by the development, growth-form and functional activities of the organisms.The gradients are present, not only in each zooid of the hydroid colony and in each tentacle of the hydranth, but in each axial complex, e.g., a compound branch, and in the colony as a whole, provided it is vigorous and growing. In general the rate and amount of reduction decrease basipetally. In the medusæ reduction is most rapid and greatest in amount in the marginal and oral regions, less in other subumbrellar regions and least in the exumbrellar region. Animals killed by other means before reaction with permanganate show no gradient, or in some cases vestiges, if newly killed. The conclusion is drawn that differences in rate and amount of reduction of permanganate, as indicated by the coloration, may, with proper precautions, be used as an indicator of differences in fundamental physiological condition in different regions of an organism.