Ahnelt P K
Vision Res. 1985;25(11):1557-67. doi: 10.1016/0042-6989(85)90126-9.
Light microscopic and histochemical studies reveal that the retina of the European ground squirrel (Citellus citellus L.) contains a mosaic pattern of two cone types and a small population of rods. A minority (7%) of the cones can be characterized by their ellipsoids having larger diameters and increased staining density over the majority population. Exposure to green light selectively elicited intense NBT-diformazan labeling in the major population of cones while the larger diameter cone type was labeled after blue illumination. The two cone subpopulations are probably the blue and green cone types of ground squirrel protanopic color vision.
