1. Triplett, E. L. J. Immun. 89, 505–510 (1962).
2. Rollins, L. A. & Cohen, N. in Development and Differentiation of Vertebrate Lymphocytes (ed. Horton, J.) 203–214 (Elsevier, Amsterdam, 1980).
3. Kobel, H. R. & Du Pasquier, L. Immunogenetics 2, 87–91 (1975).
4. DiMarzo, S. & Cohen, N. Immunology 45, 39–48 (1982).
5. Nieuwkoop, P. D. & Faber, J. Normal Table ofXenopus laevis (Daudin), 1–252 (North-Holland, Amsterdam, 1967).