1. Beach, F. A., and Jordan, L., J. Comp. Physiol. Psychol., 49, 105 (1956).
2. Bolles, R. C., Rapp, H. M., and White, G. C., J. Comp. Physiol. Psychol., 65, 311 (1968).
3. Beach, F. A., in Biological and Biochemical Bases of Behaviour (edit. by Harlow, H. F., and Woolsey, C. N.) (University of Wisconsin Press, Maddison, 1958).
4. Bogarts, R. S., Psychol. Bull., 64, 1 (1965).
5. Wang, G. H., Comp. Psychol. Monogr., 2, 1 (1923).