The presence of ribosomal DNA has been demonstrated, by light and electron microscopy study of in situ hybridization with 125I-labeled ribosomal RNA, in the Feulgen-positive bodies which appear during maturation in the cytoplasm of Xenopus laevis oocytes. The ultrastructure of these bodies is described.

Among Protozoa, the group Ciliophora (except Opalinidae) is peculiar i n having a nuclear apparatus composed of a macronucleus and a micronucleus. I t has been assumed that this nuclear dimorphism provides for a functional separation, the micronucleus serving for genetic and the macronucleus for metabolic functions only. Results of several observations and experiments during the last years indi...

Certain histologie features of virus-rich cottontail papillomas were different from those of tumors poor in virus content. The virus-rich papillomas were characterized by a marked fragmen tation of the horny layer and a well-developed granular layer which contained many keratohyalin bodies of unusually large size. A series of histochemical tests have confirmed that such large bodies are, in fac...