1. McLaren, A., and Michie, D., J. Embryol. Exp. Morphol., 2, 149 (1954).
2. Billingham, R. E., Brent, L., Medawar, P. B., and Sparrow, E. M., Proc. Roy. Soc., B, 143, 43 (1954).
3. Linder, O. E. A., Transplantation, 1, 58 (1963).
4. Kindred, B., Austral. J. Biol. Sci., 16, 863 (1963).