Photoreceptors of the larval tiger salamander retina.

Six morphological types of photoreceptor were identified with electron microscopy in radial sections of the retina of the larval tiger salamander, Ambystoma tigrinum. In order of predominance these six types are: red rods, large single cones, double cones composed of principal and accessory members, small single cones, and green rods. The different types of photoreceptor can be distinguished by a number of morphological and cytological characteristics. The identification of the small single cone type now provides evidence for more than one type of single cone in an amphibian retina. The interconnections of the different types of photoreceptor by gap junctions were studied in tangential sections. Rod-rod and rod-cone gap junctions occurred in all possible combinations, but no cone-cone junctions were found even between members of double cones.