76 



SECRETION. 

 FiG. 19. 



Arterice rectje. 



Venae rectae. 



Diagram of the Tubules and Vascular Supply of the Kidney. On the left is a tubule 

 alone ; in the middle is a tubule along with the blood-vessels ; on the right are blood- 

 vessels only. 



region of the kidney, and return (venae rectse) to join the branches 

 from the cortex and form the venae propriae of the kidney. 



How do the kidneys secrete urine ? 



(1) By filtration, and (2) by real functional action of the epi- 

 thelium. 



(1) In the circulation of the blood through the Malpighian tuft 

 there seems to be no active separation of the urinary ingredients 



