Reversible Abolition of Normal Morphology in Hydra

Abstract

THE experimental evidence concerning head and foot regeneration in hydra has been interpreted most consistently in terms of one or more gradients of unknown biochemical nature running along the length of the animal^1–5. There is also a considerable literature implicating underlying variations in “metabolic activity” in the setting up of gradients in hydra and other developing systems^6–9, but the relationship of this activity to problems of pattern formation in animal development is ill defined, because it is difficult to explain how quantitative differences in metabolic state (characterized biochemically) could be reliably distributed and translated into the qualitative differences of various cell types (see refs 10–12 for models for this process). Hydra might be particularly suited to studies in this area, because its axial pattern is simple and relatively well characterized^5,13, and regeneration and pattern regulation do not appear to require cell division¹³. The changing fates of cells within a single, organized population could ideally be followed under defined environmental influences on the metabolism.