Linkage of several pattern forming reactions to generate complex structures: head, foot and tentacle formation of the freshwater polyp Hydra as an example

The complexity of patterns in higher organisms requires a hierarchical linkage of many pattern-forming reactions. Basic arrangements are two structures that appear either adjacent to each other or at opposite poles of a field. The freshwater polyp Hydra will be used to illustrate corresponding mechanisms. The hypostome (mouth opening) with the surrounding tentacles is an example for two adjacent structures, the head foot pattern for different structures at both terminal ends (Meinhardt, 1993).