1. Yu. S. Chentsov and V. Yu. Polyakov, Ultrastructure of the Cell Nucleus [in Russian], Moscow (1974).
2. W. Bernhard, Nat. Cancer Inst. Monogr.,23, 13 (1966).
3. H. Busch and K. Smetana, The Nucleolus, Academic Press, Washington, D. C. (1970).
4. N. Granboulan and P. Granboulan, Exp. Cell Res.,38, 604 (1965).
5. J. Karasek, E. Hrdlicka, and K. Smetana, J. Ultrastruct. Res.,42, 234 (1973).