Differentiation of gonads in embryonic pigs (ages 24 to 44 days) was studied by light and electron microscopy. Incipient short cord-like structures were seen in embryos of both sexes at the age of 24 days. The cords were ultrastructurally similar. Medullary cords appeared in the testis at 26 days and in the ovary at 28 days. The cords in the ovary degenerated gradually and new cortical cords started to develop at 34 days. The formation of cords in both sexes is difficult to explain with the H-Y antigen theory, according to which the antigen should organize cords only in the male. The present results indicate that new approaches are needed for further development of the H-Y antigen theory.
Summary. Sexual differentiation and prenatal development of the gonads and the associated paramesonephric ducts were studied with the electron microscope in human and pig embryos. We wanted to elucidate the mechanisms and regulatory relationships involved in these various organogenetic events which lead to the formation of morphologically and functionally different organs from similar primordia in male and female individuals.In Introduction.
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