THE URINARY SYSTEM 



147 



stomes; and (2) the archinephric or segmental duct, which is 

 the posterior part of the tube, and runs back along the dorsal 

 body-wall nearly straight to the cloaca, into which it opens. 



The head kidney is closely surrounded by, indeed almost 

 imbedded in, the posterior cardinal vein (Fig. 37, VC), and it 

 is from the blood of this vein that the epithelial cells of the 

 NS- 



NL 



ML 



VH 



FIG. 37. Transverse section through the body of a tadpole at the 

 time of hatching ; the section passing through the second pair of the 

 ncphrostomes, and the third pair of myotomes. X 50. (From 

 Marshall's "Vertebrate Embryology.") 



A, aorta ; C, coelom or body-cavity ; CH, notochord ; CJ, sub- 

 notochordal rod ; QM, glomerulus ; KP, segmental or archinephric 

 duct ; K8, second nephrostome of left side ; ME, somatopleuric layer 

 of mesoblast ; MH, splanchnopleuric layer of mesoblast ; ML, myo- 

 tome; NL, lateral line branch of pneumogastric nerve; N8, spinal 

 cord; T, intestinal region of mesenteron ; VC, posterior cardinal 

 vein : VH, hepatic vein ; W, liver diverticulum. 



head kidney tubules separate the excretory matters, which are 

 then passed down the duct to the exterior. 



The head kidney continues to increase in size, the tubules 

 becoming still more convoluted, and lateral diverticula arising 



