ASPECTS OF GROWTH AND FORM

A model of the development of living organisms is presented which couples the geometry of the middle surface of a (closed) epithelial surface to a ''morphogen'', and the morphogen in turn is affected by the geometry of the surface in a closed system of two partial differential equations. A number of ''desiderata'' are set out for the identification of a suitable morphogen. Four parameters are involved in the model, which are assumed to be under genetic control. The morphogen is pictured as an adhesive molecule on the cell surface, and a suggestion is made for a particular molecular manifestation of this morphogen. A simple picture of gastrulation is presented as an example of the formalism.