344 



LESLIE B. AREY 



..--cn- 



TTio. iim . ex.. 



.mu. cor?. 



.my. hac. 

 .^i.ni ex. 



pa. cipf'o. 



./,, 



cr?r. 





7?? 



z./ 



//r7. ex. -. 



rn 



y 



hac. 



-Tny. con. 



1- 

 ..■st. rtl. ex. 



Fig. 1 The effect of total darkness on the position of the retinal pigment and 

 of the visual rods and cones of the fish Ameiurus nebulosus. The pigment is 

 withdrawn toward the chorioid; the cone myoid elongates, the rod myoid 

 shortens. 



Fig. 2 The effect of bright, diffuse daylight on the same retinal elements of 

 Ameiurus. The pigment moves forward toward the external limiting mem- 

 brane, thereby masking the visual rods and cones. At the right of the figure 

 the positions of these visual cells are indicated — rods elongated, cones shortened. 



ABBREVIATIONS 



chr., chorioid; 7nb.lim.ex., external limiting membrane; my.hac, rod myoid; 

 my.con., cone myoid; pd.cl.pig., base of pigment cell; scl., sclera; st.nl.ex., exter- 

 nal nuclear layer; st.pig., pigment layer. 



