1. Mitchell R. W. (1987b) Projects, routines, and enticements in interspecies play between familiar and unfamiliar dogs and people. Ph.D. dissertation, Clark University. University Microfilms.
2. Thomas R. K. & Lorden R. (in preparation) What is psychological wellbeing? Can we know if primates have it? In: The psychological wellbeing of captive primates, ed. Noyes E. F. Segal. .