Day.— Eye of Crayfish. 
PLATE 3. 
Fig. 5. Photograph of a median section of an eye exposed to yellow at 550 cm. 
for 1 min., after having been 6 hr. in dark. X 40. The pigment 
is coextensive with the tapetum (to the broken line in the left half ~ 
of the figure). 
Fig. 6. Photograph of a median section of an eye exposed to red at 550 cm. 
for 1 min., after having been 6 hr. in the dark. X45. The 
pigment is coextensive with the tapetum only about the center; 
on the sides (as indicated by the diminishing width of the dark 
band sketched into the left half) it falls short of the extent of the 
tapetum. £ 
