ABSTRACT
This chapter concerns the development of the gonads, the ovaries and testes, and the reproductive duct systems in the two sexes during the period when gonadal differentiation is being achieved. By this means, it is possible to draw attention to the so-called “indifferent” stage of organogenesis of the gonads. This is when the exclusively morphological and histological features of the gonads do not allow them to be definitively recognized as either an ovary or a testis.1,2 This equally applies to the genital duct system that is also at the indifferent stage until exposed to hormonal stimulation secreted by the gonads. These direct the components of the reproductive tract, and later the external genitalia, toward maleness if in the presence of at least a single Y chromosome or if in its absence in the “neutral” direction toward femaleness. Clearly, an analysis of the genetic sex of the individual would allow the fate of the indifferent gonad to be established, but for most purposes this information is neither needed nor, in most cases, likely to be available to the observer.
