Day.— Eye of Crayfish. 
PLATE 1. 
Fig. la. Standard light-eye: diagrammatic representation of external ap- 
pearance in daytime showing pseudopupilla. 
Fig. 1b. Standard light-eye: exposed 6 hr. to light of north window; photo- 
graph of median section, X 40. A single ommatidium sketched 
in left half: 
bm, basement membrane dp, distal retinular cells 
c, cone pp, proximal “ - 
cr, corneal hypodermis rh, rhabdome 
ct, cuticula t, tapetum 
Pigment of the proximal cells has migrated from the region below the base- 
ment membrane and has become concentrated around the nuclei in the tips 
of the cells. 
Fig. 2a. Standard dark-eye; diagrammatic representation of eye after 6 hr. 
in the dark when examined with a flash-light. 
Fig. 2b. Standard dark-eye: adapted to dark for 6 hr. and killed in the dark; 
photograph of median section. 
npp, nuclei of proximal retinular cells (drawn in ink). 
rp, pigment (13 6c 6 6c ‘ 
Retinal pigment lies mostly behind the basement membrane. The left 
half of the photograph is retouched to show the blunt processes of pigment of 
the proximal retinular cells distal to the basement membrane, which were not 
differentiated from the tapetal pigment by the camera. 
