12 ROBERT M. YERKES 



Explanation of Plate IV 



Figure 13. — Multiple-choice apparatus, showing observer's bench 



and writing stand. 

 Figure 14. — Apparatus as seen from observer's bench. 

 Figure 15. — Entrances to multiple-choice boxes as seen from 



the response-compartment. 

 Figure 16. — Apparatus as seen from the rear, showing exit 



doors, food receptacles, and covers for same. 



