[Ultrastructural evolution of fetal germinal cells to adult spermatogonia in Macaca fascicularis monkeys].

Ultrastructural changes in the spermatogonial line of the macaque, Macaca fascicularis, were studied during foetal development (from day 37), childhood and puberty. The different cell types and their distinctive morphological characteristics have been identified by studying adjacent thick and thin sections under light and electron microscopy. The main criteria used were: organization of the rough endoplasmic reticulum (RER) and its relation to mitochondria, chromatin distribution, stainability and perichromatin granule content, nucleolar organization and differentiation of the nuclear membrane including the lamina and nuclear vacuoles or cisternae. According to their ultrastructure, the following main cell classes were distinguished: gonocytes (37 to 43-day foetuses), prespermatogonia (50 to 110-day foetuses), pale type A (Ap) and dark type A (Ad) adult-type spermatogonia which differentiated progressively in 120 to 140-day foetuses. During childhood, the testis contained only Ap and Ad spermatogonia. At the onset of meiosis (about 48 months after birth), type B spermatogonia appeared, and the different classes of spermatogonia were found lying directly on the basal lamina of the sex cords. The filiation of the spermatogonial line during development has been discussed.