1. Retina pigment epithelium cells and iris pigment cells are placed in an identical medium.
2. The differentiation into two different parts, as well as the pigment strains of the migrating pigment epithelium cells, is lost. The normally highly specialized cuticular structures disappear. The cells begin to move and assume a spindle shape, thus losing their original hexagonal shape.
3. The migrating iris pigment cells begin to show a distribution of the pigment, similar to that exhibited by the migrating pigment epithelium cells. The cuticular structures of this cell type also disappear. These cells also assume the ability of free movement and become spindle-shaped.
4. By means of these changes both cell types not only become more similar to the ordinary culture cell type, but also in certain respects, more like each other, whereas before explantation they were very unlike. In order to accomplish this the pigment epithelium cells must change much more thoroughly than the iris pigment cells.
5. The changes, particularly those of the pigment epithelium cells, show a definite relation to the changes of external factors, as they are the expression of the transmission from dissimilar conditions existing on different sides of the cells into conditions which are uniform on all sides.