Explanation

Spleen and tonsils, are called secondary lymphoid organs. Lymphoid organs are categorized as primary and secondary lymphoid organs. The primary lymphoid organs are bone marrow and thymus where immature lymphocytes differentiate into antigen-sensitive lymphocytes. After maturation the lymphocytes migrate to secondary lymphoid organs like spleen, lymph nodes, tonsils, Peyer’s patches of small intestine and appendix