Summary

Numerous recent studies have clearly shown that in mammals, the radiosensitivity of germ cells changes markedly during the course of ovarian development (e.g. Rugh & Jackson, 1958; Russell, Badgett & Saylors, 1960; Beaumont, 1961, 1962). In the rat, for instance, female germ cells undergo two periods of high radiosensitivity: the first at 15·5 days post coitum, and the second some 5 days post partum. The first peak is correlated with a high incidence of oögonial mitoses, while the second coincides with the onset of the ‘dictyate’ phase of meiotic prophase (Beaumont, 1961, 1962; cf. Beaumont & Mandl, 1962). Oöcytes at the leptotene, zygotene and pachytene stages are relatively radioresistant.

Corresponding observations on oögonia and oöcytes of the developing avian embryo are scanty, and some were made before the advent of accurate dosimetry.