146 



THE FROG 



ztr.iit. 



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 ob- 

 liquely. Amongst these 

 urinary tubules or ne- 

 phridia, as they are 

 called, are seen globu- 

 lar sacs, the Malpighian 

 capsules (in. 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. 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 

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



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 ; 

 ?;z. cp. Malpighian capsule, showing epi- 

 thelium ; nst. nephrostome showing cilia ; 

 r, a. renal artery ; r, pt. v. renal portal 

 vein ; r. v. renal vein ; ur. ureter ; «?-. tu.^ 

 ur. tu'.^ «r. titj'y ur. tu."\ different portions 

 of urinary tubule, showing epithelium and 

 cilia. 



