196 



EXCRETION BY THE KIDNEYS AND SKIN 



and into it the glomerular secretion passes. The 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 



FIG. 56. Transverse section of 

 a developing Mialpighian capsule 

 and tuft (human) X 300. 



From a fetus at about the fourth 

 month; a, flattened cells growing to 

 form the capsule; b, more rounded 

 cells continuous with the above, re- 

 flected 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 a Malpighian capsule and 

 tuft. 



With the commencement of a urinary 

 tubule showing the afferent and effer> 

 ent vessels; a, layer of flat epithelium 

 forming 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, some- 

 what narrower than the rest of it. 

 (Kirkes after W. Pye.) 



are thought to be very important in secretion. The incom- 

 ing artery breaks up to form the capillary tuft; the corre- 

 sponding outgoing vein has a smaller caliber than the artery. 

 The vein, having left the glomerulus, breaks up into a sec- 

 ondary network around the convoluted tubes. This arrange- 



