ABSTRACT
The ability of four different species of Hydra to oxidize succinate has been measured. Each species studied shows a gradient in the activity of succinic dehydrogenase, which appears to be identical to the metabolic gradients described by Child & Hyman.
Each species may be recognized by its unique metabolic gradient.
The relationship between the growth-regulating system proposed by Burnett for Hydra and the metabolic gradient is discussed. The control of the level of enzyme activity is shown to be by a pair of organismal factors which are also responsible for the maintenance of polarity in Hydra.
By using the level of enzymic activity as a measure of the relative amounts of these two factors at any level in the animal, it is possible to explain the differences in form and metabolic gradient of the different species in terms of modifications in the relative amounts of the growth stimulator and inhibitor.
