146 



THE FROG 



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A thin section shows the whole kidney to be made up of 

 tangled mass of microscopic tubes (Fig. 46, //;-. tii), so 



twisted together that 

 any section cuts them 

 in various planes, some 

 transversely, when they 

 appear as circles, others 

 longitudinally or ob- 

 liquely. Amongst these 

 urinary tubules or iie- 

 phridia, as they are 

 called, are seen globu- 

 lar sacs, the Malpighian 

 capsules (/;/. cp), each 

 having in its interior a 

 little irregular bunch, 

 known as the glomerulus 

 (gl). Very accurate ex- 

 amination of numerous 

 sections, as well as of 

 teased -out specimens, 

 shows that each Mal- 

 pighian capsule (Fig. 47, 

 m. cp), is connected with 

 a urinary tubule {ur. tii), 

 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 

 glandular epithelium, which, in some parts {ur. tu, ur. tu") 



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Fig. 47. — Diagram of a 'ilngle urinary tnlml^ 

 with its blood-vessels, to illustrate the 

 structure of the frog's kidney. 

 a/.':', afferent vessel of glomerulus ; cp. capil- 

 lary network of kidney; e/.7'. effeient 

 \'essel of glomerulus ; ,^>/. glomerulus ; 

 111. cp. Malpighian capsule, showing epi- 

 thehum \ nst. nephrostome showing cilia ; 

 T.a. renal artery; 7'. pt. 7'. renal portal 

 vein ; i: z'. renal vein ; in: ureter ; nt: tu., 

 ur. hC, iir. tu." , ur. In.'", different portions 

 of urinary tubule, showing epithelium and 

 cilia. 



