  Coordinated movements of epithelia tissue are linked with active matter
processes. We here consider the influence of curvature on the spatiotemporal
arrangements and the shapes of the cells. The cells are represented by a
multiphase field model which is defined on the surface of a sphere. Besides the
classical solid and liquid phases, which depend on the curvature of the sphere,
on mechanical properties of the cells and the strength of activity, we identify
a phase of global rotation. This rotation provides a coordinated cellular
movement which can be linked to tissue morphogenesis. This investigation on a
sphere is a first step to investigate the delicate interplay between
topological constraints, geometric properties and collective motion. Besides
the rotational state we also analyse positional defects, identify global
nematic order and study the associated orientational defects.
