The duration of meiosis and spermiogenesis was studied in the dog by following the kinetics of [3H]thymidine-labeled canine spermatocytes autoradiographically. Leptotene appears to last for at least 4.20 days, zygotene for less than a day, and pachytene for about 15.50 days. The transition from diplotene to metaphase II is extremely rapid and requires approximately a day. The duration of spermiogenesis is at least 19.60 days. Both meiosis and spermiogenesis are completed by 42.15 days.

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Small pieces of ovarian biopsy from an 8-week-old human female were incubated in medium containing uridine-3H (UR-3H) for 50 min. The radioautographs of histological sections demonstrated the incorporation of uridine-3H by oocytes. Therefore, the oocyte nucleus appears to be metabolically active in RNA synthesis during the diplotene (dictyotene) stage.