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The stripes on zebras may serve as an example for pattern formation on furs or skins of fish. The original idea for an explanation can be traced back to A. Turing (1952). He suggested that in an array of originally undifferentiated cells, bio-molecules (activators and inhibitors) are produced, which may diffuse and interact with each other. In this way, a pre-pattern is formed, which, according to Wolpert (1969), represents a morphogenetic field. At high concentrations of activator molecules, genes are switched on, which then lead to a cell differentiation, giving rise e.g. to pigmentation (see e.g. Meinhardt, H. (1982), Murray, J.B. (1989)).