Blood from an individual quail embryo at stages 13-16, when primordial germ cells (PGCs) were in circulation, was taken from its marginal vein and transfused into the marginal vein of a chick embryo at stages 13-16. Both donor and recipient embryos were cultured in vitro until day 8 of development and their sex was determined by morphological and histological observations of the gonads. Sections of recipient gonads were stained immunohistochemically with QCR1 monoclonal antibody positive for quail PGCs but negative for chick PGCs. Donor and recipient embryos were sexed in 17 pairs which included all four sex combinations. Transferred PGCs, either female-derived ZW type or male-derived ZZ type, were observed in the gonads of both sexes of 15 recipient embryos. The population of donor PGCs ranged from 20 to over 2500. In all four sex combinations, there was a higher population in the left than the right gonad of the embryos.

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-In order to assess ovarian pathological changes and their relationship to changes in female fertility parameters, mifepristone, a progesterone receptor antagonist, was selected as the test article and was administered orally to female rats at dose levels of 0, 0.8, 4, 20 and 100 mg/kg for 2 or 4 weeks in repeated dose-toxicity studies and in a female fertility study at dose levels of 0, 0.8, 4 and 20 mg/kg from > 2 weeks before copulation to postcoital day 7. In the repeated dose toxicity studies, persistent estrus was seen in the vaginal smears, and multiple cysts in the ovaries at necropsy, increases in luteinized cysts and hypertrophy of previously formed corpora lutea were observed in the histopathological examination of ovaries in rats receiving 20 mg/kg or more for 2 or 4 weeks. In female fertility studies, persistent vaginal the animals were completely infertile when dosed with 20 mg/kg during the post-coital period. An increase in pre-implantation losses was observed in the animals treated with 20 mg/kg during the pre-coital phase, while treatment with 4 mg/kg mifepristone during the post-coital phase induced an increase in post-implan-

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Historical control data on rabbit prenatal developmental toxicity studies, performed between 1994-2010, were obtained from 20 laboratories, including 11 pharmaceutical and chemical companies and nine contract laboratories, in Japan. In this paper, data were incorporated from a laboratory if the information was based on 10 studies or more. Japanese White rabbits and New Zealand White rabbits were used for prenatal developmental toxicity studies. The data included maternal reproductive findings at terminal cesarean sections and fetal findings including spontaneous incidences of morphological alterations. No noticeable differences between strains or laboratories were observed in the maternal reproductive and fetal developmental data. The inter-laboratory variations in the incidences of fetal external, visceral, and skeletal alterations seem to be due to differences in the selection of observation parameters, observation criteria, and classification of the findings, and terminology of fetal alterations.