84 



Basic Structure <>f Vertebrates 

 ,r^$£ FIRST CERVICAL 



PRONEPHROS 



NEPHROGENIC. 

 TISSUE 



METANEPHROS 

 PRIMITIVE DUCT/ 



URETER 

 RST LUMBAR 



Fig. 82. A diagram of pro-, meso-, and metanephroi in a 5-6 mm. human 

 embryo. Somites are cross-hatched. (After Braus. Courtesy, Neal and Band: 

 "Comparative Anatomy," Philadelphia, The Blakiston Company.) 



brates. In some cases — e.g., Necturus — the nephrostomes persist in the 

 adult, appealing as minute holes on the ventral surface of the kidney. 

 Usually, however, the nephrostomes do not persist. In vertebrates 

 other than fishes and amphibians, the embryonic mesonephric tubule 

 ordinarily does not possess a nephrostome. The tubules of the meta- 

 nephros never acquire nephrostomes. 



An important excretory mechanism common to both mesonephric 

 and metanephric tubules is the renal or Malpighian corpuscle. The 

 tubule produces a cup-shaped expansion, Bowman's capsule (Figs. 



