Abstract
Histological examination of hybrid embryos developed by artificial insemination between female Norway rats (Rattus norvegicus, 2n=42) and male Asian type black rats (Rattus rattus flavipectus, 2n=42) was carried out with comparison between the hybrid and the control embryos which developed by artificial insemination between female and male Norway rats. Although the retardation of development of the hybrid embryo was observed, the endoderm and ectoderm were found well differentiated on the 7th and the 9th days. Until the 10th day after insemination, the hybrid embryos were clearly observed in the decidua although the development markedly delayed. The development of mesoderm was poor in this stage. On the 13th day the embryos appeared to be degenerated completely; only rudimental embryonic cells were observed in the decidua. Lethality of the hybrid embryos seemed to be due to the marked retardation of the development and differentiation.
