CHAPTER VIII 



UROGENITAL SYSTEM 



The urogenital system is composed of distinct urinary and genital glands 

 which, however, possess common ducts and have a common origin from the meso- 

 derm. The excretory glands are the pronephros, mesonepkros, and metanephros, 

 organs which develop in this order. The first two named are the temporary kid- 

 neys of the mammalian embryo, but are functional in adult fishes and amphibia. 

 The metanephros is the permanent kidney of reptiles, birds and mammals. 



THE PRONEPHROS 



The pronephros, when functional, consists of paired segmentally arranged 

 tubules, one end of each tubule opening into the ccelom, the other into a longitu- 



Antages cf 

 pronepfin'c duet 



/Vephrotome 



fronephrtc ^Coelom 

 tubuLe 



Entoderm 



Splanchnic 

 mesoderm 



\Notachord 



Fig. 197. — Diagrams showing the development of the pronephric duct and pronephric tubules (modi- 

 fied from Felix). A shows a later stage than B. 



dinal pronephric duct which drains into the cloaca (Fig. 197 A). Near the 

 nephrostome, the opening into the ccelom, knots of arteries project into the tubules, 



203 



