298 



J. B. Haycràft, 



granular tubules, which abruptly end by passing into narrower less 

 granular tubules of Henle found in the Medullary and papillary zones 



D and E. In the late embryo these con- 

 ditions are reached, except that the zones 

 B and C are not to be distinguished from 

 each other. 



Short Survey of a developing Tubule. 



In order to represent the main facts of 

 the development of a urinary tubule the dia- 

 grams (Figs. 5, 7, 15 and 16) have been con- 

 structed. In Fig. 3 the ureter is seen to end 

 in a vesicle lodged within the Kidney blastema, 

 it is dividing into two renal vesicles, joined 

 however to the ureter by stalks. In Fig-. 5 

 the vesicles have divided again and are now connected to the ureter by 

 six stalks (tubules) In Fig. 7 the vesicles are seen to be dividing and 

 throwing off urinary tubules and Malpighian bodies Mi. In Fig. 15« 



Fig. 14. 



Transverse seetion of an 



adult Kidney representing 



the position of the zones 



A, B, C and B. 



Ö 



«SV^J/7 



-Mi 



Fig. 15. 



Mi 



Fig. 16. 



one of the dividing vesicles of Fig. 7, with its stalk (tubule) and sprou- 

 ting urinary tubules is seen. In Fig. 15 ?^ this tubule has become two 

 tubules by the growth and elongation of the two primary renal vesicles, 

 which have thrown out fresh tubules and Malpigliian bodies Mil, while 

 they are still connected with those first formed Mi deeply sunk in 

 the cortex. The stalk (tubule) originally joining the vesicles with the 

 ureter has become evaginated, thus assisting in the formation of the 

 Pelvis. In Fig. 1 5 <■ one of the two tubules of !> is represented in a 



