Ultrastructure of aggregates of tumor and normal cells and of mixed aggregates. 
Contact areas have been studied in pure aggregates of either normal and malignant cells and mixed aggregates contaning both cell types.  The structures of both cell types are compared.  Tumor cells form looser connections than normal cells.  The contanct areas of tumor cells resemble those of embryonic and mitotic cells.  In a mixed aggregate sorted out, the two cell types are arranged in two regions: the "HeLa" - and the "decidua region."  The contact areas and the cells in these regions do not differ from those of the pure aggregates.  If tumor and normal cells are in direct connection with each other, they show remarkable changes: the tumor cells lose their spherical appearance as well as parts of their organelles and become ameboid.  The normal cells from a dense layer of filamentous material beneath the membrane in the neighborhood of the tumor cell.