DIFFERENTIATION OF THE NEPHROGENIC TISSUE 



203 



the buds of new collecting tubules and their parent steins (Fig. 212). One such 

 metanephric sphere is formed for each new tubule. The spheres are converted 

 into vesicles with eccentrically placed lumina. The vesicle elongates, its thicker 

 outer wall forming an .S-shaped tubule which unites with a collecting tubule, 

 its thin inner wall becoming the capsule (Bowman's) of a renal corpuscle. The 

 uriniferous tubules of the adult kidney have a definite and peculiar structure and 

 arrangement (Fig. 213 A). Beginning with a renal corpuscle, each tubule forms 

 a proximal convoluted portion, a \J-shaped loop (of Henle) with descending and 



Arch of collecting tubule 

 A' 



Proximal convoluted 

 tubule 

 Distal convoluted^ 

 tubule 

 Renal corpuscle- 

 Connecting piece 



Ascending limb of. 

 Henle's loop 



Descending limb of. 

 Henle's loop 



Large collecting, 

 tubule 



Arch of collecting tubule 



Distal convoluted tubule 



Stoerck's loop 



Proximal convoluted tubule 



Connecting piece 

 Glomerulus 



Bowman's capsule 



Arch of collecting tubule 



Proximal convoluted tubule 



Distal convoluted tubule 

 Connecting piece 

 Glomerulus 



Bowman's capsule 

 Stoerck's loop 



Fig. 213. — Diagrams showing the differentiation of the various parts of the uriniferous tubules of 

 the metanephros (based on the reconstructions of Huber and Stoerck): A, From an adult human kid- 

 ney; B, C, from human embryos. 



ascending limbs, a connecting piece, which lies close to the renal corpuscle, and a 

 distal convoluted portion continuous with the collecting tubule. These parts are 

 derived from the S-shaped anlage, which is composed of a lower, middle, and 

 upper Kmb. The middle limb, somewhat U-shaped, bulges into the concavity of 

 Bowman's capsule (Fig. 213 B). By differentiation the lower portion of the 

 lower limb becomes Bowman's capsule, ingrowing arteries forming the glomerulus 

 (Fig. 213 B, C). The upper part of the same limb by enlargement, elongation, 

 and coiling becomes the proximal convoluted tubule. The neighboring portion 

 of the middle limb forms the primitive loop (of Stoerck) ; the base of the middle 



