Minute fragments of the notochord of Balanoglossus sp. were cultivated in diffusion chambers implanted into the arm cavities of starfish, Asterias rubens. The surface properties of the cells migrating from these fragments and the intercellular contacts between them were examined in a scanning electron microscope type "Stereoscan." The two types of cell constituting the initial notochordal transplantate migrated already on the 2nd day of cultivation; these were rather large (10-12 mu) round cells with characteristic outgrowths, which grouped into colonies already on the 3rd-5th day of growth in culture, and small cells (5-7 mu) of elongated shape that at early cultivation stages were found scattered in a disorderly manner over the filter. At later cultivation stages (days 10-12), the small cells migrated toward the colonies of round notochordal cells and penetrated inside them. As a result, large colonies (counting 100 or more cells) developed in the cultures, their arrangement resembling that of the donor animal's notochord.