Germ cell development in female pouch young of the tammar wallaby (Macropus eugenii).

The cytology, timing, numbers and arrangement of germ cells in gonads of 35 female tammar wallaby pouch young aged from newborn to 210 days post partum were determined from serial sections. Germ cell cytology was essentially similar to that in eutherians. The total number of germ cells per ovary reached a peak of about 4.5 X 10(5) at 50 days and was reduced to about 25% of the maximum value by 210 days. The first oogonia developed from primordial germ cells soon after birth; the first meiotic oocytes were formed between 24 and 30 days; follicularization of diplotene oocytes began at about 50 days, and by 210 days normal, prefollicular germ cell development had ended. Successive stages of germ cells were initiated at the inner margin of the cortical region of the gonad and spread as a series of waves to the tunica albuginea. At all stages of oogonial and oocyte development many cells showed characteristic degenerative changes leading to atresia. The timing of female germ cell development in relation to gestation in tammars and humans is comparable if tammar gestation is taken to include pouch life.