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HENRY LAURENS AND S. R. DETWILER 
condition (fig. 9) the ellipsoids of the single cones are usually 
found to be on the same level as the rod elhpsoids. On the other 
hand, in the light condition (fig. 10) the cone myoid is seen to 
occupy a level closer to the external limiting membrane than that 
of the rod ellipsoid. This change in relative position is the result 
of the combined effect of rod elongation and cone contraction, 
;H \ I ? 
Fig. 9 A portion of the retina 3 mm. from the entrance of the optic nerve 
(region C). Animal in darkness for twenty-four hours. X 935. 
Fig. 10 A portion of the retina from a region corresponding to that designated 
in figure 9. Animal in diffuse light for seven hours. X 935. 
and is clearly shown by an examination of the rod and cone 
shown on the right-hand side of the diagrammatic figure 11. 
Pigment lyiigration. The differences in position of the pigment 
in light and dark eyes is slight. A series of measurements of the 
distance between the rod nuclei and the nearest pigment needle 
(table 1), as well as measurements of the distance between the 
