We prize the pearl, but in many ways the more remarkable product of molluscan manufacturing is the shell.
Many shells also display intriguing decorative patterns on their surface.
The stripes, wavy lines, chevrons, dots, triangles and other motifs are of particular interest to students of developmental biology and also to mathematicians and computer scientists. Although some of the patterns are quite elaborate, they are now understood in enough detail to reproduce their essential elements in computer simulations. In the earlier volume on plants, the algorithms chosen to describe the ramified structures of roots and stems and leaves were mostly based on recursive grammars, which model growth through the repeated application of transformational rules. Meinhardt's treatise on seashells draws on a quite different suite of mathematical tools, namely differential equations describing the creation, decay and diffusion of chemical factors that can either enhance or inhibit pigmentation. The shell grows along one edge only, where material is laid down by a row of cells at the margin of the animal's mantle.