Abstract
IT has long been known that when a cow gives birth to calves, one a male and the other a female, the male will grow into a normal bull while the female may be a freemartin. The freemartin is zygotically a female and the external genitalia and mammary glands, though modified, are usually of female type, but the gonads histologically resemble testes rather than ovaries and there is a tendency for the Wolffian ducts to persist whereas the oviducts are absent or incomplete. Fusion of the placentæ with anastomosis of their blood vessels is an essential factor in producing the freemartin. Because of the common blood supply the testicular hormones of the male have free access to the female twin and cause her reproductive organs including her gonads to conform towards the male type. Parabiosis experiments in animals and also histological examination of embryonic gonads in several species seem to show that in embryos the androgenic cells of the male gonad begin to secrete before the ovary has become completely differentiated, and that the ovary does not produce secretion until a much later stage of development. It seems also that the androgens produced in early embryonic life are abundant enough to cause profound and permanent changes in the ovaries of a female twin.
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BURROWS, H., MACLEOD, D. & WARREN, F. Excretion of Ketosteroids in Human Pregnancy Urine in Relation to the Sex of the Fœtus. Nature 149, 300 (1942). https://doi.org/10.1038/149300a0
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DOI: https://doi.org/10.1038/149300a0
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