1. Hendrickson, J. R., Proc. Zool. Soc., 130, 455 (1958).
2. Mrosovsky, N., and Shettleworth, S. J., Behaviour (in the press).
3. Carr, A., and Ogren, L., Bull. Amer. Mus. Nat. Hist., 121, 1 (1960).
4. Carr, A., and Hirth, H., Anim. Behav., 9, 68 (1961).
5. Bustard, H. R., Nature, 214, 317 (1967).