Lymph node from a Siberian tiger cub afflicted with congenital thymic aplasia (analogous to human Di George syndrome). A number of primary follicles (PF) are visible directly under the capsule. However, the diffuse cortex (DC) below, which should be filled with the blue-staining nuclei of T-lymphocytes, is largely empty and shows the pink staining of the underlying connective tissue. At the bottom is the more open region representing the medulla (M).