1. Zeuthen, E., Pubb. Stazione Zool Napoli, Symposion ( May 1951, in the press).
2. Hoff-Jørgensen, E., Biochem. J. (in the press).
3. Rugh, R., “Experimental Embryology” (Minneapolis, 1948).
4. Graff, S., and Barth, L. G., Cold Spring Harbor Symposia, 6, 103 (1938).
5. Lison, L., and Pasteels, J., Arch. Biol., 62, 2 (1951).