1. Abercrombie, M., “Contact inhibition: the phenomenon and its biological implications.” Nat. Cancer Inst. Monograph 26, 249–277 (1967).
2. Ansevin, K. K., and R. Buchsbaum, “Observations on planarian cells culturated in solid and liquid medial.” J. Exp. Zool 146, 153–161 (1961).
3. Arakilian, P., “Cyclic oscillations in the extinction behavior of rats.” Jour. Gen. Psychology 21, 137–162 (1939).
4. Beling, I., “Über das Zeitgedächnis der Bienen.” Z. vergl. Physiol. 9, 259–338 (1929).
5. Best, J. B., and I. Rubinstein, “Environmental familarity and feeding in a planarian.” Science 135, 916–918 (1962b).