  Cross-streamline non-inertial migration of a vesicle in a bounded Poiseuille
flow is investigated experimentally and numerically. The combined effects of
the walls and of the curvature of the velocity profile induce a movement
towards the center of the channel. A migration law (as a function of relevant
structural and flow parameters) is proposed that is consistent with
experimental and numerical results. This similarity law markedly differs from
its analogue in unbounded geometry. The dependency on the reduced volume $\nu$
and viscosity ratio $\lambda$ is also discussed. In particular, the migration
velocity becomes non monotonous as a function of $\nu$ beyond a certain
$\lambda$.
