The architecture of the spleen of the yellow‐bellied toad, <i>Bombina variegata</i>

The spleen of the yellow‐bellied toad, Bombina variegata , consists of distinct white and red pulps. The well‐developed white pulp is formed by a large central lymphocytic region around the numerous blood vessels and by its smaller peripheral ramifications, both surrounded by the more or less developed connective tissue boundary layer. Large peripheral sinuses of the white pulp, filled mostly with lymphocytes, are usually present at the inner side of this boundary. At the outer side of the boundary layer, the lymphocytic marginal zone is often observed. This zone merges into the erythrocyte‐rich red pulp formed by cellular cords and small venous sinusoids. The structure of the spleen of Bombina variegata differs considerably from the spleens of other anuran species studied so far. The highly developed white pulp and its distinct separation from the red pulp may be connected with the important role of the spleen as the main secondary lymphoid organ of B. variegata. The splenic compartmentalization makes the yellow‐bellied toads a useful model for experimental immunobiological studies.