METHODS OF STUDYING VISION IN ANIMALS 



61 



seen here from the back at Sg and Sr. These two slits admit 

 the two selected beams, e.g., red and green. 



The track 5 supports five i" square iron posts, 20, 21, 22, 



Figure 9 — Perspective of the color selecting, snacing and reversing device. The 

 selected bands are admitted through the sht openings, Sg and Sr. Tliey are 

 brought near together by total reflection prisms 18 and 19, reversed by prisms 

 54 and 55 and focussed by the small lenses 45, 4G and 47. The beams are 

 spaced by the prisms 40 and 41. 



23, 24, 25, which are first shouldered on their lower end so as 

 to fit the opening between the bars forming track 5, and are 

 then turned down to form a |"-i2 screw. A knurled nut, 26, 



