In a simple two-compartment system, the behaviour of a flip-flop can be obtained by reversible reduction of selective membrane permeability. The behaviour corresponds to a triggerable reversal of “differentiation” of the two-cellular system. The model is identical with the simplest Rashevsky- Turing system, that is a two-compartment system showing spontaneous differentiation if the selective permeability for one constituent is raised above a critical value. The identity is not accidental and can be interpreted as an example of Rosen’s principle of function change. The phenomenon may be used for an empirical test of the Rashevsky-Turing theory of morphogenesis