1. Jennings, H. S., Behavior of the Lower Organisms (Indiana University Press, Bloomington, 1962).
2. Thompson, R. F., Foundations of Physiological Psychology (Harper and Row, New York, 1967).
3. Adler, J., Science, 166, 1588 (1969).
4. Hazelbauer, G. L., Mesibov, R. E., and Adler, J., Proc. US Nat. Acad. Sci., 64, 1300 (1969).
5. Hazelbauer, G. L., and Adler, J., Nature, 230, 101 (1971).