1. J. Sterzl andM. Hrubesova, Fol. Biol.2, 21 (1956).
2. M. Hrubesova, B. A. Askonas, andJ. M. Humphrey, Nature183, 97 (1959).
3. A. B. Stavitsky, Brit. J. Exp.39, 46 (1958).
4. J. D. Ebert andW. J. van Doorenmaalen, Ann. Report, Carnegie Inst. Washington, Dept. Embryology (1958–59), p. 399.
5. B. D. Jankovic, K. Isakovic, andJ. Horvath, Nature183, 1400 (1959).