... predicted by the polar coordinate model. We propose that dishevelled encodes an intracellular protein required to respond to a wingless signal and that this interaction is essential for establishing both cell polarity and cell identity. * Author for correspondence The sequence of dsh suggests...

.... There is evidence that positional signals within a single animal and in related animals are conserved. It is not clear just how wide this conservation is, but it is at phylotypic stages, rather than in eggs, that similarity might be expected. It is nevertheless impressive that the polar coordinate model can...

... are discussed in the light of two current models describing the developing chick limb and analysed diagrammatically within the framework of one of these models, the polar coordinate model. * Present address: Developmental Biology Center, University of California at Irvine, Irvine, California 92717, U.S.A...