Introduction

Much has been written and more has been said about putative fundamental concepts or philosophies of biological growth and development. These range from the ‘mechanics' of Wilhelm Roux, and the ‘determinants' of August Weismann in the latter part of the nineteenth century, to the elegance of simple geometrical transformations as pronounced by D'Arcy Thompson (1917). Contemporary view include the notion that living systems are dynamic, self-evolving structures popularised by Prigogine and Turing (Harrison, 1987). Conceptually attractive as these latter views are, they are not easily accessible experimentally, and it seems that the most dramatic advances have taken place in molecular genetics/biology. This has undeniably permitted us a glimpse of some of the most fundamental processes of morphogenesis (Ingham, 1988). Despite the evident fecundity, however, a true molecular picture of the elemental mechanisms of differentiation is not attainable exclusively from molecular genetics. It is necessary to address the problem from a physical and physiological point of view as well as from these more established genetic-based approaches. This is perhaps exemplified best by the approach of Williams and co-workers (Perry, Wilcock & Williams, 1988) who emphasise, and indeed demonstrate, that morphogenesis is a process of many interconnecting physical, electrical, chemical and genetic processes. Thus, multi-disciplinary approaches are necessary to understand the many interactions which constitute growth and development (O'Shea, 1988a). Here I shall barely mention the role that differential gene activity may play in morphogenesis (which in any case is probably very familiar to most developmental biologists).