1. Austin, C. R., and Bishop, M. W. H., in The Beginnings of Embryonic Development (edit. by Tyler, A., van Borstel, R. C., and Metz, C. B.), 71 (Amer. Ass. Adv. Sci., Washington, 1957).
2. Bishop, D. W., Amer. J. Physiol., 187, 347 (1956).
3. Siegler, A. M., Fert. and Ster., 4, 495 (1953).