Day.— Eye of Crayfish. 
PLATE 2. 
Fig. 3. Photograph of a median section of an eye exposed to blue-violet at 
a distance of 550 cm. from the light-box for 1 min., after having 
been 6 hr. in the dark. Xx 36. The pigment reaches to the 
nuclei of the retinal cells. 
Fig. 4. Photograph of a median section of an eye exposed to green at 550 cm. 
for 1 min., after having been 6 hr. in the dark. X 40. The 
pigment has migrated beyond the tapetum (indicated by broken 
line in left half of the figure), but not out to the nuclei. 
