The three sections of the kidney develop at different stages, starting with the pronephros and ending with the metanephros. |
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The pronephros, developing early in embryo formation, is the functional kidney of fish and amphibian larvae. |
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The tubules empty into a long tube, the Wolffian duct, a remnant of the pronephros. |
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In reptiles, birds, and mammals, the pronephros is nonfunctional, although even in these animals its duct persists as the mesonephric duct. |
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The mammalian pronephros is a rudimentary vestigial structure. |
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The mesonephros develops later and replaces the pronephros as the functional kidney of adult fishes and amphibians and of the embryos of reptiles, birds, and mammals. |
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