Abstract
1. A preparation consisting of an oyster mantle and its attached shell has been devised for in vitro studies of shell formation. Shell consisting of typical organic matrix and birefringent crystalline material was elaborated by this preparation, though at a slower rate than in the intact oyster. 2. All parts of the mantle were shown to be capable of shell formation in vitro. 3. The isolated mantle-shell preparation can be maintained in good condition for several days.