UROGENITAL ORGANS. 



IIQ 



participate in its formation. From this time on the prone- 

 phric duct is usually called the mesonephric or Wolffian duct. 

 The aorta likewise forms segmental twigs, which grow out to- 

 wards the splanchnic layer of the nephrotome, and give rise 

 to a series of vascular networks, the glomeruli, which differ from 

 the glomus of the pronephros in that they project not into the 

 larger body cavity (splanchnoccele), but into the cavity of the 



mb, 



P l 



FIG. 127. Diagram of the development of the nephridial system in the verte- 

 brate. The pronephric system is according to the views of Semon ; it is more prob- 

 able that they arise from the nephrotomes instead of from the somatic layer, a, 

 aorta; c, notochord ; <<-, cardinal vein; </, pronephric duct; g, glomus ; ^w, gonad; 

 ;, intestinal epithelium; ///, myotome (muscular layer); mb, Malpighian body; me, 

 myocoele; mt, mesonephric tubule; , nephrotome; ns, nephrostome ; pf, prone- 

 phric tubule; sc, spinal cord; sg, spinal ganglion; sm, sympathetic ganglion; so, 

 somatic layer ; sp, splanchnic layer ; z, cavity of nephrotome. Compare with Fig. ill. 



nephrotome, and in their segmental arrangement. The walls 

 of the nephrotome close over each glomerulus, and are hence- 

 forth known as Bowman's capsule, while the whole complex of 

 capsule and glomerulus form a Malpighian body or corpuscle. 

 The mesonephric tubule opens into Bowman's capsule by means 

 of an inner nephrostome, while the lower portion of the nephro- 



