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Ovarian autografts were performed on the omentum in 3-week~ld hemicastrated rats. The second ovary was removed after 10, 30,60 and 90 days. At the same time a bilateral oophorectomy together with an implantation of ovarian autografts were performed in control animals of the same age. In some of the animals, operated for the second time after 30, 60 and 90 days, a fragment of the removed ovary was implanted near the first graft. The animals were killed 1 and-2 months after total castration and the mean weights of the implant were compared between rats with a single graft and controls. In animals with two implants the second one served as a control and the mean weights of the two grafts were compared. In hemicastrated animals the implants remained "dormant" and did not grow during 6 months of observation. However, their histological picture suggested some gonadotropic influence. The mean weights of the implants in the bilaterally castrated control animals declined steadily with increased age of the rats at the time of operation. In the experimental animals with one implant, the decrease was noted only in the group castrated 30 days after hemicastration. No further decline in the mean weights of implants was found in animals castrated 60 or 90 days after hemicastration. In rats with two implants, the fust implant behaved as in experimental animals with one implant, while the mean weights of second implants declined progressively as in the control animals. The results obtained suggest that the decline in the growth capability of ovarian implants is a biphasic phenomenon. The fust phase-observed in rats be fore puberty-is conditioned by the aging of ovarian tissue, while the second phase-noticed in rats after pubertyis, in some way, influenced by the functional alterations occuring in the ovary at that time.

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