292 



■T. B. Hay craft, 



Diagrammatic view of 



the Kidney of a 13 days 



rabbit. 



have become irregular cavities spreading out in a direction parallel 

 with the cortex and distinctly branching or dividing. In addition one 

 may see two or three little structures budding out from each of them, 

 these are the urinary tubules with their Mal- 

 pighian bodies: the whole Kidney is diagramma- 

 tically represented in Fig. 7 and the formation 

 of a tubule and Malpighian body in Fig. 8. The 

 tubules and Malpighian bodies arise as buds of 

 solid cells from the wall of the primary renal 

 vesicles close to the cortex, the bud makes a 

 double bend like an S, first turning with a large 

 sweep away from the vesicle, then turning to- 

 wards it and then sharply away again. The 

 Basement membrane can be traced along it and 

 a central lumen forms almost to its tip. As 

 subsequent study will shew, these little sprouts 

 form the whole urinary tubules, for 

 the tubules which branch from the 

 ureter and terminate in the primary 

 renal vesicles, become evaginated to 

 form the pelvis of the Kidney, and 

 their epithelium will in subsequent 

 embryos be found lining its cavity. ^) 

 Each little sprout from the renal ve- 

 sicles will, in other sections of older 

 embryos, be seen to elongate, the 

 bulging portion marked H will grow 

 down towards the forming pelvis to 

 form the convoluted tubules and a 

 loop of Henle, the part at ik/, marks 

 the formation of the future Malpigh- 

 ian body. At this stage there is 





Fig. 8. 



High power view of the tirst forma- 

 tion of a urinary tiibule from a pri- 

 mary renal vesicle V. The tubule 

 makes an S shaped bend and at M. de 

 Malpighian body is forming. 



') In no way therefore can the first branches of the ureter be said to form 

 the collecting tubules, for they become turned inside out and their epithelium be- 

 comes that of the pelvis. 



