A light microscopic study of the retina of the nurse shark, Ginglymostoma cirratum, and the sting ray, Dasyatis sayi, demonstrated two types of receptors which had the main morphological characteristics of rods and cones. The rods were very similar in both species but
the cones differed slightly—those of Dasyatis were more cone-like than those of Ginglymostoma. The ratio of rods to cones was 7:1 for Ginglymostoma and 5:1 for Dasyatis.
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