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THE reproductive system of the fowl undergoes remarkable changes at sexual maturity at which time a weight increment of several thousand percent occurs in both the oviduct and ovary in-side a few weeks. It is also well established that a very large increase in weight of the oviduct in the adult fowl occurs when egg laying recommences following periods of ovarian inactivity and that many of the changes which take place as a hen comes into lay can be simulated by the injection of sex hormones into immature pullets. These effects of sex hormones in birds have been reviewed by Parkes and Em-mens (1944) and Lorenz (1954). The injection of oestrogen will evoke an increase in oviduct size and changes in blood composition, although the ovaries remain quiescent. The production of lipaemia in birds by the administration of oestrogens has been confirmed by variou