1. X. Chardonnens andL. Du Pasquier, Eur. J. Immun.3, 569 (1973).
2. N. Bernardini, X. Chardonnens andD. Simon, C. r. Acad. Sci., Paris D269, 1011 (1969).
3. P. D. Nieuwkoop andJ. Faber,Normal Table of Xenopus laevis (Daudin) (North Holland Publishing Company, Amsterdam 1956).
4. L. Du Pasquier, X. Chardonnens andV. C. Miggiano, Immunogenetics, in press.
5. A. Reynolds, inHormones in Development (Eds.M. Hamburgh andE. J. W. Barrington; Appleton Century Crofts, New York 1971), p. 299.