1. The snark was a boojum;Beach;Am. Psychol.,1950
2. Student behavioral research in zoos;Beck,1975
3. Ethology — the zoologist's approach — Part I;Beer;Tuatara,1963
4. Ethology — the zoologist's approach — Part II;Beer;Tuatara,1964
5. Object play and social treatment of prey in bush dogs and crab-eating foxes;Biben;Behavior,1982