Abstract
The collapse of shell-shaped membranes due to buckling is investigated experimentally using droplets of latex suspension left to dry. The evaporation of water, limited by diffusion in air, first leads to the formation, on the surface, of a spheroidal envelope of gel. During the later evolution, spontaneous buckling of this envelope occurs. The later evolution leads to a large-amplitude invagination and for certain concentrations to a transition to a toroidal shape. This specific evolution of a spheroidal envelope, linked with its inhomogeneous mechanical properties, is similar to that observed during the gastrulation of sea-urchin embryos.