146 



THE FROG 



CHAP. 



ur.tit 



A thin section shows the whole kidney to be made 

 up of a tangled mass of microscopic tubes (Fig. 



46, ur. tu), so twisted 

 together that any 

 section cuts them in 

 various planes, some 

 transversely, when 

 they appear as circles, 

 others longitudinally 

 or obliquely. Amongst 

 these urinary tubules or 

 nephridia, as they may 

 be called, are seen 

 globular sacs, the 

 Malpighian capsules 

 (m. cp}, each having in 

 its interior a little 

 rounded bunch, known 

 as the glomerulus (gl). 

 Very accurate examin- 

 ation of numerous sec- 

 tions, as well as of 

 teased-out specimens, 

 shows that each Mal- 

 pighian capsule (Fig. 



47, m. cp) is connected 

 with a urinary tubule 

 (ur. tu), to which it 

 forms a blind, bulb- 

 like end. The tubule 

 itself winds through 

 the substance of the 

 kidney, is joined by 



other tubules, and finally discharges into the ureter (ur) . 

 The tubules are lined with somewhat cubical cells of 



FIG. 47. Diagram of a single urinary tubule 

 with its blood-vessels, to illustrate the 

 structure of the Frog's kidney. 

 af. v. afferent vessel of glomerulus ; cp. capil- 

 lary network of kidney ; ef. v. efferent 

 vessel of glomerulus ; gl. glomerulus ; 

 m. cp. Malpighian capsule, showing epi- 

 thelium (which in reality also covers the 

 glomerulus) ; nst. ciliated nephrostome ; 

 r. a. renal artery ; r. pi. v. renal portal 

 vein ; r. v. renal vein ; ur. ureter ; ur. tu, 

 ur. tu', ur. tu", ur. tu'", different por- 

 tions of urinary tubule, showing epithelium 

 and cilia. 



