196 



EXCRETION BY THE KIDNEYS AND SKIN 



outer layer is the capsule of Bowman (or Miiller) . Both layers 

 consist of a single stratum of flattened epithelial cells; those of 

 the inner layer are applied closely to the glomerulus and are 

 thought to be very important in secretion. The incoming artery 

 breaks ap to form the capillary tuft; the corresponding outgoing 



FIG. 56. Transverse section of a 

 developing Malpighian capsule and 

 tuft (human.). 



From a fetus at about the fourth 

 month ; a, flattened cells growing to form 

 the capsule; b, more rounded cells con- 

 tinuous with the above, reflected round 

 c, and finally enveloping it; c, mass of 

 embryonic cells which will later become 

 developed into blood-vessels. (Kirkes 

 after W. Pye.) 



FiG.57. Epithelial elements of 

 Malpighian capsule and tuft. 



With the commencement of a urinary 

 tubule showing the afferent and efferent 

 vessels; a, layer of flat epithelium form- 

 ing the capsule; b, similar, but rather 

 larger epithelial cells, placed in the walls 

 of the tube; c, cells, covering the vessels 

 of the capillary tuft; d, commencement 

 of the tubule, somewhat narrower than 

 the rest of it. (Kirkes after W. Pye.) 



vein has a smaller caliber than the artery. The vein, having 

 left the glomerulus, breaks up into a secondary network around 

 the convoluted tubes. This arrangement of the Malpighian body 

 furnishes a most favorable opportunity for the passage of sub- 

 stances out of the blood current into the beginning of the tube. 



