At the beginning of the 20th century, the cytoplasmic bodies which appear in the lymphoid tissues of mammals had received much attention of haematologists, in the relation to the origin of the blood platelets. However, since Wright described and figured in 1910 the process of cytoplasmic budding of megakaryocytes by the use of his own technics, the biological significance of the cytoplasmic bodies in the lymphoid tissues has been ignored until now. Recent works on the formation of antibodies in the lymphoid tissue seem to suggest, on the other hand, that these bodies would play an important role in the immune response. Consequently, we attended a renewed study of these bodies. In this paper we described the results of histochemical observations on these bodies in, the mesenteric lymph node and thymus of adult mice. The chief findings are as follows: 1. Cytoplasmic bodies are found in large number in the mesenteric lymph node of adult mice. They also occur in the thymus, though in much smaller numbers. 2. Cytoplasmic bodies in the thymolymphatic tissues vary greatly in size, from the size of blood platelets to that of small lymphocytes, and are commonly round in shape. They often contain pyroninophilic granules. 3. Staining of these bodies with methyl green-pyronin and acridine orange revealed that they contain abundant RNA. However, no evidence was obtained for the presence of DNA in these bodies. 4. After digestion of the samples with RNase, the pyroninophilia of these bodies disappeared completely. This suggests that the pyroninophilic granules of these bodies might be regarded as ribosomes.