The effect of laboratory environment on the morphology of the spleen and the thymus in the yellow-bellied toad, Bombina variegata (L.).

The morphological changes were observed in the spleen and the thymus of the yellow-bellied toad, Bombina variegata, kept under standard laboratory conditions. The mean splenic weights of toads studied soon after capture in July and September were 16.0 mg and 17.7 mg, respectively. In contrast, the mean splenic weights significantly decreased in animals maintained in the laboratory from July till September (to 11.6 mg) and from July till December (to 6.8 mg). In the spleen of toads kept in the laboratory the lymphocyte aggregations were diminished in the white pulp while the amount of connective tissues increased both in the white and in the red pulps. Melano-macrophages were more abundant in the red pulp of toads kept in the laboratory than in freshly collected ones. The thymuses of toads kept in the laboratory were decreased in size and depleted of the majority of their cortical lymphocytes. It is suggested that the morphological changes of the yellow-bellied toad lymphoid organs might be the results of stressful laboratory conditions and lower antigenic stimulation in the laboratory than in nature.