[Anomaly of the nuclear maturation in vitro of golden hamster oocytes]

Nuclear anomalies were observed during maturation in vitro of golden hamster oocytes, as follows: 1) In 33 p. cent of oocytes, the axis of the first meiotic division spindle was oriented incorrectly. This leads either to the formation of "large" polar bodies or to non-expulsion of the polar body if the spindle occupied a central instead of peripherical position. 2) Triploidy was observed in 0.3 p. cent of the oocytes which accomplished their maturation and fertilization in vitro. 3) Two rare anomalies--reconstitution of the nucleus after expulsion of the first polar body and formation of two second division spindles--appeared to be due to degenerescence of the oocytes in culture.