The survival of goat \ m=x\ sheep hybrid embryos in goats carrying hybrids for the first time was compared to that in goats which had carried hybrids in previous breeding seasons and in goats sensitized against sheep antigens. The findings on the goats carrying hybrids for the first time showed that embryonic death occurred during the 6th week of gestation; twelve live embryos (crown-rump lengths, 22 to 36 mm) were recovered from seven goats examined on Days 35 to 38 of pregnancy, and eight dead embryos (crown-rump lengths, 20 to 38 mm) were recovered from six goats at Days 38 to 43. The size of dead embryos (crown-rump lengths, 7 to 11 mm) recovered from four of five goats carrying hybrids for the second time suggests that survival did not extend much beyond the 3rd week of gestation. Six goats which had received skin grafts and injections of leucocytes from the sheep used for insemination were examined at Days 35 and 36 of pregnancy; live embryos (crown-rump lengths, 25 to 26 mm) were recovered from two goats, and dead embryos (crown-rump lengths, 10 to 16 mm) were recovered from four goats.

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The experiments described below were undertaken to study the effects of different hormone treatments on follicular development, ovulation and fertilization in lambs. In a similar investigation, Mansour (1959) obtained a low rate of fertilization which he attributed to the use of diluted semen and to the inefficiency of insemination by the vaginal route. In the present experiments fresh undiluted semen was introduced directly into the uterine horns.Sixteen Scottish Blackface and eight crossbred female lambs were used. The average weight was 16\m=.\7 kg (range 11\m=.\5to 26\m=.\5 kg). The treatments were begun (Day 0) as soon as possible after the lambs were 50 days of age so that ovulation would be expected to occur when the lambs were approximately 9 weeks old.

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