抄録
Two types of photoreceptors were present in both Dasyatis akajei and D. navarrae which were easily differentiated morphologically into rods and cones at the microscopic level. The lack of cones was found in another 7 species of sharks. Instead they showed exclusive domination by retinal rods.
Physiological follow-up investigations using S-potential showed that Dasyatis akajei gave the chromatic (C) response to S-potential. No trace of the C-response was observed in the retinae of four species of sharks.
From these observations the ability to discriminate color is thought to exist in the Dasyatis whereas the sharks in all probability are color blind.
All these species gave the L-response to S-potential, in which maximum wavelength was found at 494nm in sharks and at 525-548nm in Dasyatis. The former closely corresponds with the absorption maxima of visual pigments of shallow-sea sharks.
