The period of ovulation in mature house musk shrews was examined in a natural mating group and a superovulation group treated with gonadotropin. In the natural mating group, ovulation started 14 hr after mating in 3 of the 7 house musk shrews (42.8%), and occurred in all 5 house musk shrews by 15 hr after mating. In the superovulation group, ovulation started 13 hr after the administration of hCG in 3 of the 5 house musk shrews, and was observed in all 5 shrews by 16 hr after the administration. In the natural mating group, ovulated ova were collected from the ovarian bursa of 14 house musk shrews 14-20 hr after mating (mean, 2.2 +/- 1.0 ova) and from the oviduct of 42 animals 14-24 hr after mating (mean, 3.6 +/- 1.8 ova). Among the ova ovulated 14-16 hr after mating, both mature ova with the first polar body and immature ova without the first polar body were observed. In the superovulation group, ovulated ova were collected from the ovarian bursa of 31 house musk shrews 13-22 hr after the administration of hCG (mean, 9.7 +/- 6.8 ova), and from the oviduct of 28 animals 13-24 hr after the administration of hCG (mean, 20.0 +/- 11.7 ova). There were also mature and immature ova in the ova ovulated 13-16 hr after the administration of hCG. The time when ova ceased to be recovered from the ovarian bursa roughly coincided with the time when new corpora lutea ceased to be found in the ovaries. These findings suggested that the period of ovulation of house musk shrews was 14-20 hr after mating in the natural mating group and 13-22 hr after the administration of hCG in the superovulation group. Both the natural mating group and superovulation group ovulated both mature ova with the first polar body and immature ova without the first polar body.
