Genital ridge derived from which mesoderm?

Each testis develops from the coelomic epithelium, that covers the medial side of the mesonephros, of the corresponding side. In the region where testis is to develop, this germinal epithelium becomes thickened. This thickening is called the genital ridge. The gonadal ridge (or genital ridge) is the precursor to the gonads. The gonadal ridge initially consists mainly of mesenchyme and cells of underlying mesonephric origin. Once oogonia enter this area they attempt to associate with these somatic cells.The gonadal ridge appears at approximately five weeks, and gives rise to the sex cords. (Reference : I B Singh's Embryology, 10th edition , pg 307)