The testicular cords are preserved also in the medulla of the gonad. They converge towards the hilum of the gonad into a region of loose mesenchymal tissue in which the rete blastema arises. From month 4, the testicular cords gradually develop a lumen and thus become the seminiferous tubules. They end into the excretory duct of the mesonephros through a network-like system of channels (rete testis) and 5-12 mesonephric tubules.
A layer of connective tissue forms between the testicular cords and the surface epithelium, called the primary tunica albuginea. This gives rise to the definitive tunica albuginea, consisting of dense connective tissue. Small septa grow from this tissue into the interior of the testicle, subdividing it into lobules of the testis.