1. Weiss, P., and Kavanau, J. L., J. Gen. Physiol., 41, 1 (1957).
2. Bullough, W. S., and Laurence, E. B., Exp. Cell Res., 33, 176 (1964).
3. Rytomäa, T., and Kiviniemi, K., Cell Tissue Kinet., 1, 329 (1968).
4. Nieukoop, P. D., and Faber, J., Normal Table of Xenopus laevis (Daudin) (North-Holland Publishing Co., Amsterdam, 1967).
5. Bullough, W. S., Hewett, C. L., and Laurence, E. B., Exp. Cell Res., 36, 192 (1964).