SUMMARY The morphometabolical development of the thymus has been studied in the pre and postnatal ontogenesis in pigs. The studies pointed that the thymus is organized early in the prenatal period, at about two months of pregnancy. The histochemical investigations pointed out an intense secretory activity for the reticulo ephitelial cells and for the thymic corpuscles. The histological investigations in prenatal period revealed a massive presence of thymic corpuscles and the existence of some peculiar cellsmyoid cells, whose number rises parallel to the development of the organ. At the growing age it is certain that the thymus does not experience an entire involution; part ofthe functions are maintained in some secretory and hematopoetical insulary cells.
thymus; reticuloepithelial cells; thymic corpuscles; myoid cells