1. Introduction; 2. The evolutionary origins of play revisited: lessons
from turtles G. M. Burghardt; 3. Play in common ravens (Corvus corax) B.
Heinrich and R. Smolker; 4. Object play by adult animals B. Heinrich and R.
Smolker; 5. Kangaroos at play: play behaviour in the Macropodoidea D. M.
Watson; 6. Intentional communication and social play: how and why animals
negotiate and agree to play M. Bekoff and C. Allen; 7. The
structure-function interface in the analysis of play fighting S. M. Pellis
and V. C. Pellis; 8. Sparring as play in young pronghorn males M. N. Miller
and J. A. Byers; 9. Squirrel monkey playfighting: making the case for a
cognitive training hypothesis M. Biben; 10. Self assessment in juvenile
play K. V. Thompson; 11. Biological effects of locomotor play: getting into
shape, or something more specific? J. A. Byers; 12. Neurobiological
substrates of play behaviour: glimpses into the structure and function of
mammalian playfulness S. M. Siviy; 13. Play as an organizing principle:
clinical evidence and personal observations S. Brown.
