A comparative study of the ultrastructure of the different segments of rods and cones in the retina of the rabbit was presented. The similarities in the general pattern of organization of both photoreceptors will be stressed. The presence of a “connecting cilium” (J. biophys. biochem. Cytol. 3, 319 (1956)] in the cone cells is indicative of a morphogenetic origin of the outer segment similar to that previously described for the rod [J. biophys. biochem. Cytol. 2, 209 (1956)]. Both the outer segments of the rods and cones are built of double membranous flattened sacs, but the dimensions of the membrane and the interspaces are definitely different. Some of these data were discussed on the basis of the concentration of solids of the outer segment and the relative position of protein and lipid, within the membrane of the sac. The comparative fine structure of the inner segment and of the synaptic region is described.