  Morphologies of a vesicle confined in a spherical vesicle were explored
experimentally by fast confocal laser microscopy and numerically by a
dynamically-triangulated membrane model with area-difference elasticity. The
confinement was found to induce several novel shapes of the inner vesicles,
that had been never observed in unilamellar vesicles: double and quadruple
stomatocytes, slit vesicle, and vesicles of two or three compartments with
various shapes. The simulations reproduced the experimental results very well
and some of the shape transitions can be understood by a simple theoretical
model for axisymmetric shapes.
