Abstract
Semen of the black rat was inseminated artificially into the female Norway rat by routine technique. Among 20 rats, 9 showed pregnancy. Five impregnanted rats were dissected on 8 to 14 days after insemination and one to 4 embryos were found. No offspring were born in the case of the artificial insemination. In the control in which the semen of the Norway rat was inseminated artificially into the female Norway rat, pregnancies were obtained at high frequency and offspring were successfully born as in natural matings. Chromosomes of the hybrid blastocysts showed 42 chromosomes consisting of two haploid sets, one from the Norway rat and the other from the black rat.
