True hermaphroditism in chimaeric mice

Abstract

Histological examination of the reproductive systems of fourteen newborn chimaerae developed from fused eggs revealed eleven sexually normal animals and three true hermaphrodites. The genital apparatus of the hermaphrodites is described, the structure of the gonads being given special attention. Of the three hermaphrodites, one had one ovary with female sex ducts and an ovotestis with complete male ducts and incomplete female ones. The second had two ovotestes and a genital apparatus of nearly typically male type; the remnants of Müllerian ducts being retained only caudally. The third had one ovary with female sex ducts and one ovotestis with male sex ducts. The occurrence of true hermaphrodites strongly suggests that spontaneous true hermphroditism also develops from sex-chromosome mosaicism. The available literature on spontaneous hermaphroditism in rodents is critically reviewed. It is postulated that the frequencies of the four types of true hermaphroditism described (ovary-testis, ovary-ovotestis, testis-ovotestis, ovotestis-ovotestis) in mice and other rodents do not adequately reflect their actual incidence in nature in that the incidence of the lateral type of hermaphroditism is exaggerated. It is suggested that if the testicular tissue does, in fact, elaborate a morphogenetic stimulus influencing the differentiation of XX gonadal tissue, such a stimulus must be rather weak and act only near the site of its elaboration. The genetic sex of germ cells in chimaeric hermaphrodites remains unknown. It is postulated that the presence in the hermaphrodite gonads of oöcytes and male germ cells reflects only the secondary differentiation of germ cells, which need not reflect their genetic sex. While the ovarian tissue of the ovotestes examined contains only oöcytes, in the testicular tissue both oöcytes and spermatogonia are present. Initiation of meiosis of the female type in the testicular territory is attributed to the action of a meiotic stimulus elaborated by the ovarian tissue and diffusing through the testicular part.