1. Martin, G. R. (1975).Cell 5:229?243.
2. Graham, C. F. (1977). InConcepts in Mammalian Development, (ed.) Sherman, M. I. (The M.I.T. Press, Cambridge, Massachusetts), pp. 315?394.
3. Stevens, L. C. (1959).J. Natl. Cancer Inst. 23:1249?1295.
4. Pierce, G. B., Dixon, F. J., and Verney, E. L. (1959).Cancer 12:573?583.
5. Martin, G. R., and Evans, M. J. (1975).Cell 6:467?474.