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Figure 1 — The figure is symmetrical, hence the letters G, E, L, and S must be 

 understood to designate both the parts which they respectively mark and 

 also duplicates of these parts on the opposite side of the figure. 



1. Hover box: O, hover box; G, inclined planes (which were replaced by 

 wooden platforms) of mesh wire leading from the doors, E, of the experiment 

 box to the hover box. 



2. Illumination box: H, left compartment; P, right compartment; L, 

 lamps; S, metric scales. 



3. Experiment box: A, compartment in which chick was placed; C, com- 

 partment in which it made choice of screens; B, gateway between A and C. 

 D and D', electric passageways; N, and N.j, illuminated glass screens to be 

 discriminated; E, openings to platforms at the sides of the experiment box; 

 M and M', cardboard shutters for closing these openings; U and R, electric 

 keys for extinguishing lamps in H and P, respectively; K, stimulus key; I, 

 inductorium. 



