Chap, x^x.i KIDNEY, URETER, AND BLADDER. 239 



according to the thickness of the tube ; each cell 

 possesses a flattened oval nucleus next to the lumen, 

 and a very coarsely and conspicuously fibrillated pro- 

 toplasm. 



312. (11) This irregular tubule passes into the 

 distal convoluted tubule or intercalated tubule of 

 Sclrweigger Seidel. This forms one of the convoluted 

 tubes of the labyrinth, and in size, aspect, and 

 structure, is identical with the proximal convoluted 

 tubule. 



(12) The distal convoluted tube passes into a 

 short, thin, more or less curved or wavy collecting 

 tubule, lined with a layer of transparent, flattened, 

 polyhedral cells ; this is still contained in the laby- 

 rinth. 



(13) This leads into a somewhat larger straight 

 collecting tube, lined with a layer of transparent poly- 

 hedral cells and with distinct lumen. This tube 

 forms part of a medullary ray, and on its way to the 

 boundary layer takes up from the labyrinth numerous 

 curved collecting tubules. 



(14) It then passes unaltered as a straight collect- 

 ing tube through the boundary layer into the papillary 

 portion. 



313. In this part these tubes join under acute 

 angles, thereby gradually enlarging. They run in a 

 straight direction towards the apex of the papilla, 

 and the nearer to this the fewer and the bigger they 

 become. These are the ducts or tubes of Bellini. 

 They finally open on the apex into a calix. The lumen 

 and the size of the lining epithelial cells viz., whether 

 more or less columnar are in direct relation to the size 

 of the collecting tube. The substance of the epi- 

 thelial cells is a transparent protoplasm, and the 

 nucleus is more or less oval. 



314. In many places nucleated cells, spindle- 

 shaped or branched, can be traced from the mombrana 



