TJie development of the kidney in the rabbit. 2!)9 



more advanced stage of growth; the vesicle has divided again forming 

 a third urinary tubule and Malpighian body Miii. In Fig. 16 the 

 adult condition is reached — only a few tubules are represented — 

 and the primary renal vesicles have contracted to the diameter of a 

 urinary tubule. 



Conclusions. 



1. That the connective tiussue and bloodvessels of the Kidney de- 

 velop from the blastema, while the epithelium of the tubules 

 proliferates from the cells originally lining the ureter and Wolf- 

 fian duct. 



2. The tubules which first sprout into the blastema terminate in 

 dilatations the primary renal vesicles. 



3. Then these form branching irregular cavities which always re- 

 main at the periphery of the cortex, from these the urinary 

 tubules bud off, the older ones sinking down into the medulla. 



4. The tubules which first sprout from the ureter and terminate in 

 the vesicles soon become turned inside out to form the pelvis of 

 the Kidney. 



5. Many of their prolongations into the rapidly dividing renal 

 vesicles aiso become evaginated, thus increasing the number of 

 tubules passing between the pelvis and the renal vesicles at the 

 cortex. 



6. Those that remain form the collecting tubules. 



7. The Bowman's capsule is moulded into its shape upon the bent 

 portion of its own tubule, long before the glomerulus is formed 

 It is invaginated therefore rather by its tubule than by the 

 glomerulus. 



8. The 5 zones which in the adult rabbit's Kidney differ both 

 physiologically and histologically from each other, are only repre- 

 sented in the late embryo by 4 layers. 



