STRUCTURE OF THE VERTEBRATES 



255 



and the Bowman's capsule together are known as a renal or 

 Malpighian corpuscle. In amniote embryos the nephrostomes 

 rarely, if ever, break through into the coelomic cavity. 



The mesonephros is the functional kidney of the cyclostomes, 

 fish and amphibia. It appears as a large body in amniote embryos 

 and was first described by the anatomist Wolff. As a result of 

 his discovery the mammalian mesonephros is known as the 

 Wolffian body, and the mesonephric duct as the Wolffian duct. 

 In the amniotes the mesonephros is merely a transitory embryonic 



Draining 

 tubule 



Fia. 142. Development of the 

 Metanephros. The metanephric 

 out pocketing is shown in contact 

 with the nephrotome. Compare 

 Fig. 118 for the earher stages. 



Bowman^s 

 capsule 



Glomerulus 



Fig. 142-a. The Development of 

 Collecting Tubules. The pelvis 

 divides, the tubules joining the 

 nephrogenic tubules (right). 

 (From preparations by R. T. 

 Kempton). 



structure. A part of it, however, remains in the male in connec- 

 tion with the reproductive system. The metanephros is the func- 

 tional kidney of the amniotes. 



]\Ietanephros. The metanephros and its draining ducts have 

 a double origin. The renal corpuscles and the outer ends of the 

 tubules arise from the primitive nephric anlagcn, the nephro- 

 tomes, and are serially homologous with the mesonephric and 

 pronephric kidneys which arise more anteriorly. The ureters and 

 collecting tubvles which drain the kidneys arise as paired out- 

 pocketings from the posterior ends of the mesonephric ducts. Im- 

 mediately anterior to the fusion of the mesonephric ducts an 



