FIG. 1.

Idealized timing of the first wave of spermatogenesis. The time line from birth onward indicates the temporal sequence of events in the first 35 days pp (27). Intervals in which mitotic cell division, meiosis I, meiosis II, and spermiogenesis occur are indicated above the time line, noting different stages during prophase of meiosis I. Spermatogonia populate the seminiferous tubules after birth, giving rise to spermatocytes, spermatids, and spermatozoa, as indicated below the time line.