True hermaphroditism in chimaeric mice

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Abstract
In a preliminary communication on the development of mouse chimaerae formed from fused eggs (Tarkowski, 1961) three cases of intersexuality were reported among newborn animals. Sexing was based exclusively on macroscopic examination of the reproductive system. The present paper deals with the microscopic structure of this system in chimaeric hermaphrodites, with special reference to the structure of the gonads. The occurrence of intersexes among animals developed from fused eggs was considered as one of the proofs of their chimaeric constitution (Tarkowski, 1961). Abnormalities similar to those displayed by these chimaerae have been described in the mouse and related rodents in sporadic spontaneous cases of hermaphroditism. However, while the genesis of the latter is unknown, there are strong indications that hermaphroditism among chimaerae develops on the basis of sex-chromosome mosaicism. This type of mosaicism can be expected a priori to occur in a number of individuals developed from two eggs randomly selected.