Day. — Eye of Crayfish. 



PLATE 5. 



Fig. 9a. Observation record of eye 141, dark 6 hr. Color, yellowish orange. 

 Pronounced darkening in tiie upper half. 



Fig. 9b. Section of eye 141, X 41. The extent of the migration is about 

 twice the width of the tapetal layer, but not out to the nuclei. 



Fig. 10. Photographic test of light-box for leakage of white light. A Seed's 

 "Gilt Edge 27" plate, substituted for the animal as in text-fig. F, 

 had six separate exposures made on it as follows: At 50 cm.: a, 

 30 sec; b, 60 sec; c, 90 sec At 150 cm.: d, 270 sec; e, 540 sec; 

 f. 810 sec. 



