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Abstract
The pigmented and neural portions of the retina develop as separate layers and are free to slide over one another during the first half of development. Despite the fact that they follow different schedules of mitosis, cell death, and cell hypertrophy, these layers correspond in area throughout development. Descriptive and experimental findings in the chick embryo suggest the following explanation. After closure of the choroid fissure, vitreous substance accumulates in the vitreous cavity, resulting in rapid groioth of the eye. Tensile forces thus generated at the level of the retina have little effect on the neural retina, which increases in area relatively independently of these forces. The pigmented epithelium, however, increases in area only in response to these forces. The expansion in area of the pigmented epithelium is, in large part, the result of cellular hypertrophy. Since the growth of the individual cells is dictated by the rate of expansion of the vitreous body, the pigmented epithelium is, at any stage of development, very closely tailored in its area to the size of the eye and of the neural retina.