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Abstract
Photoreceptor cells in guinea pig retinas begin to shed their outer segments while developing in utero. To ascertain whether phagocytosis of outer segments in the fetus is a cyclical event like that of mature animals, large phagosomes in fetal retinal pigment epithelial cells were counted at representative times during a 24 hr period. These data were then compared with similar data obtained from the pregnant dams. Gravid animals and fetuses both showed a burst of shedding after the onset of illumination. Shedding was well initiated in the pregnant animals 30 min after the onset of illumination but was delayed for 2 to 3 hr in their fetuses. Thereafter the two patterns of phagocytosis showed substantial differences. Congruent cyclical patterns could be discerned, however, by graphing fetal counts with an advance of 10 hr on the time scale relative to that of the gravid animals. The results presented here represent the first indication of a cyclical pattern of phagocytosis in a population of fetuses during retinal development.