The rabbit's appendix is a pecular lympho-epithelial formation as it includes both areas of thymus-dependent lymphocytes (the interpolated sieved lamina) and non-thymus-dependent lymph nodes. The epithelium joining the intestine lumen and the lymphatic tissue contains cells that become permeable at the contact of lymphocytes. These "tranformed" enterocytes are crossed by antigenic molecules, bacteria, yeasts and evolutive forms of coccidia. Lymphocytes within--as well as reticular cells below the epithelium--catch large molecules, especially antigens, thus having a share in humoral immunity. Just as those of the intestine, the enterocytes of the appendix glandular area are informed at the level of the areas of epithelial mitosis and become resistant to certain infections such as coccidosis. This particular form of immunity we have named "epithelial immunity". Thick sections provide ultrastructural views physically showing information exchanges. Intercellular exchange by contiguous endoplasmic reticular canaliculi at the interface of two cells have thus been demonstrated. They have been as clearly observed between two epithelial cells at between two cells of connective origin and again between an epiethelial cell and a lymphocyte.