IX.—Gynandromorphism and Lateral Asymmetry in Birds

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Abstract
Shortly after Juhn, Faulkner and Gustavson (1931) had shown that natural differentials in the growth‐rate of individual feathers on one and the same fowl determined, in part, the threshold of their response to œstrin, the faster the growth‐rate the greater being the amount of œstrin required to produce female feathering, Lillie (1931) extended their conclusions to a re‐examination of the cases of lateral gynandromorphism in birds recorded in the literature up to that time. He pointed out that this condition seemed always to be associated with lateral size asymmetry, and argued therefore that, since the male side was the larger and presumably the faster growing, to account for lateral gynandromorphism it was necessary only to postulate that the ovary of the bird should be malfunctioning, producing a sub‐normal amount of œstrin, sufficient to evoke henny‐feathering on the smaller, more slowly growing side, but insufficient to do so on the larger, faster growing side.