1. Beatty, R. A., Institute of Animal Genetics, Edinburgh, Research Report 1952–54, 25 (1955).
2. Johansson, I., and Hansson, A., Ann. Agric. Coll., Sweden, 11, 145 (1943).
3. Wallace, L. R., J. Agric. Sci., 38, 93 (1948).
4. Yeates, N. T. M., J. Agric. Sci., 39, 1 (1949).
5. Robinson, T. J., J. Agric. Sci., 41, 275 (1950).