The presence of an extracellular matrix between cells involved in the determination of the mesoderm bands in embryos ofPatella vulgata (Mollusca, gastropoda).

In 32-cell stage embryos ofPatella vulgata one of the macromeres contacts the animal micromeres, and as a result is induced to differentiate into the stem cell of the mesodermal cell line. In this study we show the presence of an extracellular matrix (ECM) between these two interacting cell types. The ECM appears to be formed by the micromeres during the 32-cell stage.