Changes

===The Mesonephros===

===The Mesonephros===

This structure forms in the thoracic and lumbar regions and is important in embryonic life.  It has more tubules than the pronephros and the structure of these tubules is similar to that of the adult kidney. They are closed at one end and open at the other.  The open end drains into the pronephric duct which is now more appropriately called the mesonephric duct.  The closed end has a bundle of capillaries which form a filtration mechanism.  This organ is variable in size in relation to how efficient the placenta is at removing waste.  The worse the placenta the bigger the organ.  As the metanephros develops it supersedes this organ and it begins to regress as a result.  Parts of it do, however remain in the male and form part of the reproductive tract.

This structure forms in the thoracic and lumbar regions and is important in embryonic life.  It has more tubules than the pronephros and the structure of these tubules is similar to that of the adult kidney. They are closed at one end and open at the other.  The open end drains into the pronephric duct which is now more appropriately called the mesonephric duct.  The closed end has a bundle of capillaries which form a filtration mechanism.  This organ is variable in size in relation to how efficient the placenta is at removing waste.  The worse the placenta the bigger the organ.  As the metanephros develops it supersedes this organ and it begins to regress as a result.  Parts of it do, however remain in the male and form part of the ductus deferens.

===The Metanephros===

===The Metanephros===