Germ cell kinetics in the neonatal rabbit testis.

Germ cells in the developing rabbit testis were found to undergo several distinct changes in the first two weeks after birth. Mitotic activity, which had been high in the late fetal period, reached a peak on the day before birth, then diminished steadily and ceased entirely after five days of age. Extensive germ cell degeneration occurred in the first week after birth resulting in accumulation of pools of degenerating germ cells in the central portions of the cells at various stages of preleptotene could be found in squash preparations. This corresponded to the time when germ cells in the rabbit ovary enter and proceed through meiotic prophase. There was no evidence of entry into leptotene or later stages of meiosis in the neonatal testis. The findings suggest that a similar stimulus for entry into meiosis may exist in both sexes, but a blockage occurs in the male.