ABSTRACT
The emergence of definite organ and tissue structure during development implies that the component units—cells and intercellular materials—assume patterned space relations. These reveal themselves in geometric features of position, proportions, orientation, grouping, alignment, and so on. The ordering processes involved are variously referred to as ‘organization’, ‘differentiation’, ‘morphogenesis’, ‘field action’, and the like. Such terms, while useful as identifying labels for the respective problems, are largely lacking in concrete operational meaning. To realize this, one need only consider how little is known about the practical devices and tools by which any given product of development is achieved. The study of the ‘biotechnology’ of developmental mechanisms has indeed been lagging behind the preoccupation with general principles.
