The ultrastructure of developing and differentiating retinal cells of chick embryo was studies during the early embryonic period from 33 hours old till 6 days old. At 33 hours old, the optic vesicle was 2-3 cells thick. The cells had almost the same form. At 48 hours old, the outer wall of the optic cup became thinner than the inner wall. Retinal cells of chick embryo were mitotically active during the first six days of incubation. It was impossible to distinguish photoreceptor cells from each other during the first three days of incubation. Slimming of the pigmented retina is suggested to be due to apoptosis. The first sign of differentiation was observed at the age of three days, where photoreceptors started to show up. The basal bodies of cilia were formed. The cilia were completely differentiated at the age of six days. Cilia were at the apices of photoreceptors invading the optic ventricle but not tightly attached to the pigment epithelium. Different stages of mitochondrial differentiation were seen. Mitochondriogenesis is suggested in the present study to be de nove. Not all the cells were differentiated at the age of six days. Photoreceptors and pigment epithelial cells were the first types to be observed.