Parthenogenetic development of mouse embryos in vivo. II. Postimplantation development.

CBA-p and CBA-T6T6 females were mated with vasectomized males of A strain and early in the morning the eggs were activated in situ with the electric shock of 30, 40 and 50 V. Females were killed between the 5th and the 10th day of pregnancy and the implantation sites were studied histologically or their content was examined under the dissecting microscope. Of the uterine horns, 43-6 % contained at least one implantation and the mean number of implantations per horn was 0-76. Altogether 152 implantations were collected. The implantation rate was twice as high in older females (12 weeks and over) as in young ones (6-8 weeks). The number of living embryos decreased with every day so that on the 9th and 10th day only 2 out of 86 embryos were alive (2-3 %). With one exception all embryos which were alive at the time of examination were retarded in development for approximately 1 day. The most advanced embryo was at the 8-somite stage. Two attempts aimed at increasing the synchrony between the embryos and the uterus at the time of implantation (activation immediately after delayed mating and transfer of 4-5-day embryos to 3-5-day uterus) did not improve the survival of embryos after implantation.