Shell patterns - a natural picture book to study dynamic systems and biological pattern formation -- Pattern formation by local self-enhancement and long range inhibition -- Oscillations and traveling waves -- Superposition of stable and periodic patterns -- Crossings, meshwork of oblique lines and staggered dots: the combined action of two antagonists -- Branch initiation by global control -- The big problem: two or more time-dependent patterns that interfere with each other -- Triangles -- Parallel lines with tongues -- Shell models in three dimensions -- The computer programs -- Pattern formation in the development of higher organisms -- Pattern formation in development in which shell-related mechanisms are implicated.