Introduction

Abstract

If you have been fortunate enough to see a film of the development of any multicellular organism or, better still, to watch live embyros developing, the intricate beauty of the developmental process will not have escaped you: nor will its complexity. Apparent complexity, however, is no reason for despair when one begins to think in terms of analysing development. Rather, it is a stimulus to the first and most important analytical step, that of simplifying the problem by dividing it into aspects which can be meaningfully studied.