HISTOLOGICAL AND HISTOCHEMICAL STUDIES ON THE PRONEPHROS & MESONEPHROS OF RATS EMBRYOS

The pronephros in rats embryos appeared at the 11 th day of fetal life as two protruded masses on both sides of the primitive aorta. Each mass was formed of primitive renal tubules and renal corpuscles and surrounded externally by simple cuboidal epithelium . Nucleated red blood corpuscles were showed between the primitive renal tubules. The cranial part of the pronephros disappeared while the caudal part was formed . The pronephric tubules are completely disappeared at 12 day of fetal life and the pronephric duct was remained as mesonephric duct . The first appearance of the mesonephros was noticed at 12 day of fetal life caudal to the pronephros . The mesonephric tubules are separated from each other by mesenchymal cells and showed internal invaginations on their free ends and connected to the mesonephric duct at the other end . The renal corpuscles appeared at 13 day foetal life with internal glomeruli. At 14 day of fetal life ,the mesonephric tubules begin to degenerate cranially and this degeneration was completed at 16 day of fetal life while the mesonephric duct was remain. The abscence of the positive histochemical reaction in our results may be attributable to the short duration of pregnancy.