16 



ROBERT M. YERKES 



RB 



Figure 1. — Left half of medium sized reactive tendency apparatus. (1) 1-6, reac- 

 tion mechanisms or boxes; En, entrance door; Ex, exit door; (2) RC, reaction 

 chamber; (3) rb, release box; rd, door between release box and reaction cham- 

 ber; (4) A, A, alley from reaction boxes to release box; D, door between alley 

 A and release box; X, center of circle on arc of which reaction boxes are placed. 



