The pearl: isolation of outside bodies by molluscs: evolution of the graftand the pearl-sac in Pinctada margaritifera (Mollusca, Lamellibranchia)

The production of a cultured pearl needs a 'graft', i.e. the introduction i nto the receiver nacre's pearl pocket of an aragonite bead and a mantle pie ce from a donor nacre. The contribution of the external epithelium of the g raft is essential to the constitution of the pearl sac. This secretory shea th is produced within about twenty days; it is monocellular and exhibits fo ur cell types. The other tissues of the graft rapidly degenerate. Conjuncti ve and hemocytic reactions of the receiver mollusc are described.