“…Before this period, the seminiferous epithelium is formed by Sertoli cells (which end their mitotic activity just before entering into sexual maturation) and type-A spermatogonia. At puberty, and due to many factors not yet fully understood, the pattern of spermatogonial renewal and proliferation, followed by spermatogenic differentiation ensues, as is characteristic of complete (adult) spermatogenesis (Bustos-Obregon et al, 1975). The effect of irradiation upon full spermatogenesis has been addressed by many authors (in the rat : Dym & Clermont, 1967;Pineau et al, 1989; in mice : Oakberg, 1956: Oakberg, , 1959Bustos-Obregon & Rodriguez, 1990).…”