1. Kindred, J. E., Amer. J. Anat., 67, 99 (1940).
2. Kindred, J. E., Amer. J. Anat., 71, 207 (1942).
3. Fichtelius, K. E., in Ciba Found. Symposium on Haemopoiesis, edit. by Wolstenholme, G. E. W., and O'Connor, M. (Churchill, 1960).
4. Metcalf, D., in The Thymus in Immunobiology, edit. by Good, R., and Gabrielson, A. E. (Harper and Row, 1964).
5. Sainte-Marie, G., and Leblond, C. P., Proc. Soc. Exp. Biol. N.Y., 98, 909 (1958).