IG 



Devclopiueiit and .Sha}x' ol' L'riiiircvous Tubules 



than above discussed, in that the primary branches had already under- 

 gone secondary division. In these drawings, the nephrogenic tissue, for 

 the sake of clearness, is not included. The models are purposely shown 

 from different aspects, the one (A) giving a lateral view, the other (B) 

 a dorsal view with reference to the position of these structures in the 

 respective embryos. In both figures, in A more clearly than in B, the 

 three pairs of primary branches are still discernible. The bulbous ex- 

 tremities of the primary renal pelvis descril3ed for earlier stages show 

 here a division into branches, more clearly seen in B than in A, the former 

 representing a slightly older stage. 



Fig. 1. Wax reconstruction of the ureter, primary renal pelvis, and 

 branches. X 50. A, cat embryo (No. 2), 13 mm. in length ;B. human embryo 

 (No. 5), neck-breech, 16 mm., head-breech, 20 mm. In each figure only about 

 one-third of the length of the ureter is represented. 



The primary branches of the renal pelvis, or, as they may hereafter be 

 known, the primary collecting tubules (Nierengangaste — Schreiner), ex- 

 tend to near the periphery of the renal anlage. Each shows, as has been 

 stated, a distal enlargement, which is known as the ampulla (primitive 

 renal vesicle — Haycraft), and which is surrounded by a cap of tissue 

 which we have described as the inner zone of the metanephrogenic tissue. 

 Each ampulla, in its further development, enlarges, the distal wall of the 

 enlargement becoming somewhat flattened and two lateral buds are de- 

 veloped; the primary collecting tubule now presents the appearance of a 

 T or a Y when seen in longitudinal section or in a reconstruction. The 

 distal end of each bud, soon after its beginning, develops a new ampulla. 

 The inner zone of the metanephrogenic tissue which surrounds the pri- 

 mary ampulla as a continuous cell-mass, begins to show a separation into 



