1. Kramer, G., Naturwissenschaften, 37, 377 (1950).
2. Montgomery, K. C., and Heinemann, E. G., Science, 116, 454 (1952).
3. Waterman, T. H., Proc. Fifteenth Intern. Cong. Zool. Lond., 537 (1959).
4. Dill, P. A., thesis, Univ. British Columbia (1965).
5. Groot, C., Behaviour, Suppl. 14 (Brill, Leiden, 1965).