The occurrence of cytoplasmic bodies in lymphoid tissues of mammals was first described by Downey and Weidenreich (1912). Concerning the significance of occurrence of these bodies, however, little is know at present. In the present study, the mode of occurrence of these bodies in imprints and sections of lymphoid tissues of rabbits, mice and young chickens was investigated, in relation to the functional differentiation of lymphoid tissues into the central and the peripheral ones. The chief findings are as follows: 1. In the peripheral lymphoid tissues, such as lymph nodes and spleen (splenic white pulp), cytoplasmic bodies of varying size are found in large numbers, whereas they are scanty in the central lymphoid tissues such as the thymus, although in the appendix and sacculus rotundus of rabbits, as well as in the bursa of Fabricius of young chickens, they are not so few as in the thymus. 2. Cytoplasmic bodies stained red by methyl green-pyronin, after fixing in Carnoy's fluid. They are chiefly composed of pyroninophilic granules or threads. They vary greatly in size, from the size of blood platelets to that of small lymphocytes. After digestion of the samples with RNase, the pyroninophilia of these bodies disappeared completely. Feulgen reaction is negative in these bodies. 3. In the lymph nodes and spleen, which had previously been stimulated by antigen, cytoplamic bodies occurred in much greater numbers than in the unstimulated control tissues.