1. Barski, G., Sorieul, S., and Cornefert, F. R., CR Acad. Sci., 251, 1825 (1060).
2. Ephrussi, B., and Sorieul, S., Approaches to the Genetic Analysis of Mammalian Cells, 81 (Univ. of Michigan Press, 1962).
3. Weiss, M. C., and Green, H., Proc. US Nat. Acad. Sci., 58, 1104 (1967).
4. Matsuya, Y., Green, H., and Basilico, C., Nature, 220, 1199 (1968).
5. Harris, H., Watkins, J. F., Ford, C. E., and Schoefl, G. I., J. Cell Sci., 1, 1 (1966).