At present embryos are frozen for long-term preservation. But this method is not easy to carry out because of the complexity of the equipment and procedure required and the many problems yet to be solved. The authors studied the possibility of unfrozen low-temperature preservation of embryos for a short period by keeping them at 5-8 °C. As a result, it was found that embryos at the 8-16 cell stage were well preserved in serum-added geratine solution. The optimal serum concentration was 33.3%, and the addition of gelatine had a favorable effect. When rabbit embryos at the morula stage were preserved in rabbit oviducts, they survived up to 7 days in nearly all the cases, while mouse embryos preserved in rabbit oviducts were not viable. When rabbit embryos were preserved in blood vessels, viable embryos were obtained up to 5 days from more than half the cases. These embryos were transfered, and they were proved normal embryos because they yield young. The above-mentioned findings indicated that this method could be put to practical use with detailed studies of the oval stage, medium, and enviroment optimal for embryo preservation.

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In an attempt at collection of an increased amount of follicular ova, superovulation was induced in prepuberal, sexually immature calves (8-12 weeks old) by intramuscular injection of 1500 iu of PMSG followed 5 days later by intravenous injection of 1500 iu of hCG. The ovaries were removed by laparotomy at 24 hours after hCG treatment. The ovaries from one animal contained 70 follicles above 10 mm in diameter, 13 follicles 9-5 mm and 145 follicles above 2mm. The ovaries from the other animal contained 86 follcles'measuring more than 2 mm in diameter. The in vitro fertilization exper-iment using the collected follicular oocytes resulted in 58.2% sperm penetration and 44.9% fertilization with female and male pronuclear formation. The results suggested that ovaries from prepuberal cattle have a hicrher Potentiality for ova.

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Mouse embryos were cultured in vitro in media containing Act-D, PM or CHX during the interval from the 2-cell stage to the early blastocyst stage. Two-or 4-cell stage embryos cultured in the presence Act-D developed to the 4-or 8-cell stagel, respectively, but further development did not occured. Act-D at l0^-1 ug/ml inhibited development of morula. PM and CHX inhibited completely the development in vitro of the embryos.

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