Arthropod Cuticle

Experiments with the limbs of amphibians, roach legs, and fly wing disks suggested to French et al. (1976) some simple rules governing growth and pattern formation in the insects and in higher animals. To apply these rules (Chapter 16), we must first find a point on a ring associated with each point on the animal’s two-dimensional surface. French et al. argue that morphogenesis is conducted primarily within two-dimensional sheets of cells and that within these sheets cells know their identity in part as a point on a ring, which we might think of as an angle or a phase. The pattern of phase (together with a second, independent quantity) across the two-dimensional sheet determines the qualitative pattern of growth and differentiation. In particular, phase singularities play a crucial role, for example determining the number and handedness of limbs (Glass, 1977).