Examples of heritable information storage in structure other than nucleic acid include the inheritance of changes in the cortex of Paramecium aurelia11 and other ciliates and in the cell wall of Bacillus subtilis.12 Phenomena similar to those observed in ciliates may also occur in the cortex of eggs.13 Evidence of information storage in molecular activity or concentration rather than structure include induction phenomena such as the galactosidase permease system in E. coli14 where either of two alternative stable steady states may be inherited to an extent independently of external inducer concentration. Mathematical analysis demonstrates that these properties can be explained by feedback systems.15,16 Other inherited phenomena which may involve feedback mechanisms or stable association of macromolecules with germline DNA include serotype transformation in Paramecium,17 environmentally induced changes in flax18 and tobacco,19 inheritance of the scrapie agent20 and extinction phenomena in rotifers.21 It must be emphasised that by the criterion of heritable information the alternative states of an operon system store information in addition to that stored in the nucleic acid sequences involved in the feedback circuitry.