The development of singed ovaries transplanted to wild type females in the late larval stage shows autonomous development. Eggs recovered from such females have the characteristic shape of eggs from singed females and they fail to give rise to larvæ. Wild type ovaries grown in singed hosts likewise show autonomous development. Viable eggs can be recovered from such ovaries; they give rise to wild type offspring (females heterozygous for wesn) when fertilized by wesn sperm. Fused ovaries grown in singed hosts have characteristics not detectably different from such ovaries grown in their normal position. Recovered eggs fertilized by fu or by Y sperm fail to hatch, but those fertilized by not-fu X-carrying sperm give rise to normal females heterozygous for fu. Ovaries from female-sterile females grown in wild type hosts may become attached to the oviducts of the hosts, competing successfully with normal ovaries, but they remain rudimentary as they do in their normal genetic surrounding. Wild type ovaries grown in female-sterile females show autonomous development. Viable eggs giving normal development are recovered following attachment of the implant to the oviduct of the host. Using a single outcrossed stock of wesn and two wild type stocks, one outcrossed and one inbred, reciprocal ovary transplants show: (1) that the frequency of attachment of the implant varies with different genetic stocks, and (2) that, under the conditions of the experiments and with the numbers involved, there is no statistically significant difference in the frequency of implant-attachment in reciprocal transplants. Transplants in which donors and recipients were different in absolute age show that the frequency of attachment of the implant can be varied, either increased (in certain combinations) or lowered, by varying the relative ages of donors and recipients. In one combination in which ovaries were implanted to hosts younger than the donors, there was apparently a lethal interaction such that most of the hosts died after pupation. The bearing of the age-difference experiments on the differences in frequency of implant-attachment observed with different stocks is considered. The application of certain of the results summarized above to the use of gonad transplants in Drosophila as an experimental tool are pointed out.