The growth of the retina has been studied in Xenopus by use of autoradiography with tritiated thymidine. At the time when retinal polarization first occurs (around stage 30) there are only some 20 ganglion cells across the retinal equator and the rest of the retina develops later, by annular addition of cells at the ciliary margin. This process continues beyond metamorphosis.
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Straznicky et al. (1971) studied this question.
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