  We study the effects of delayed coupling on timing and pattern formation in
spatially extended systems of dynamic oscillators. Starting from a discrete
lattice of coupled oscillators, we derive a generic continuum theory for
collective modes of long wavelength. We use this approach to study spatial
phase profiles of cellular oscillators in the segmentation clock, a dynamic
patterning system of vertebrate embryos. Collective wave patterns result from
the interplay of coupling delays and moving boundary conditions. We show that
the phase profiles of collective modes depend on coupling delays.
