1. Hamilton, L., J. Embryol. Exp. Morphol., 22, 253 (1969).
2. Flickinger, R. A., Miyagi, M., Mour, C. R., and Rollins, E., Develop. Biol., 15, 414 (1967).
3. Lawrence, P., Symp. Soc. Exp. Biol., 25, 379 (Cambridge University Press, London, 1971).
4. Kihlman, B. A., The Action of Chemicals on Dividing Cells 96 (Prentice Hall, 1966).
5. Nieuwkoop, P. D., and Faber, J., Normal Table of Xenopus laevis (Daudin) (North Holland, Amsterdam, 1956).