488 



CHORDATA. 



type occurring most abundantly in the posterior part of the mesonephros, 

 and leading some to regard this portion as a metanephros. 



The metanephros, in its typical form as it appears in the amniotes, 

 consists of two anlagen. A canal grows out from the Wolffian duct, 

 extends cranialward, and branches richly at its anterior end. The canal 

 is the ureter, the tubules arising from it are the so-called straight tubules 



B 



777 q 



\s 



Ho- 



Ov.Z 



FIG. 539. Scheme of urodele urogemtal system based on Triton (from Wieders- 

 heim, after Spengel). A, male; B, female, a, excretory ducts; gn, sexual part of meso- 

 nephros; Ho, testis; Ig, Leydig's duct (ureter); nig, Miillerian duct (oviduct); ing', its 

 vestigial end in male; N, functional part of mesonephros; Ov, ovary; Ot, ostium tubte; 

 Ve, vasa efferentia; *, collecting duct of vasa efferentia (rudimentary in B). 



of the kidney. The other part of the organ consists of tubules, which 

 arise from 'nephrogenic tissue,' have no nephrostomes, but include a 

 Malpighian body at the end. The other end connects with the straight 

 tubules. They form the convoluted tubules of human histology. 



