348 THE UEINAEY SYSTEM 



are rather more distinct. Basal striations are also less distinct than 

 in the convoluted tubule, the lateral serrations less deep, and the 

 cell outlines sharper. The cells of this portion frequently possess 

 a slightly imbricated arrangement. 



7. The Distal Convoluted Portion (Intercalary or Intermediate 

 Portion, Convoluted Tubule of the Second Order). This portion 

 of the uriniferous tubule begins close to the vascular pole of the 

 Malpighian body, and, after several irregular contortions which 

 are confined to the region of the cortical labyrinth, enters an 

 arched collecting tubule. The distal is much shorter than the 

 proximal convoluted portion. Its caliber is subject to great 

 irregularities, so much so that its early turns have been charac- 

 terized as the irregular or zigzag portion of the uriniferous tubule. 

 The epithelium of this section resembles that of the proximal 

 convoluted portion but is lower, more cuboidal, and striations are 

 indistinct. 



This portion terminates the typically secretory portion of the 

 uriniferous tubule. Beyond here the tubule possesses more the 

 function of a duct, hence its epithelium shows a decided change 

 in character. Hitherto it has possessed the peculiar character, 

 the typically granular cytoplasm, of a secreting type of cell. Be- 

 yond this section the epithelium is no longer so granular but pos- 

 sesses a characteristically clear appearance. 



8. The Arched Collecting Tubule (Curved or Junctional Tubule). 

 This is a short portion of the uriniferous tubule which connects 

 the distal convoluted portion in the cortical labyrinth with the 

 straight collecting tubules of the medullary rays. Its course is 

 characteristically arched. 



The epithelium of the arched tubule consists of clear cuboidal 

 cells with distinct outlines and deeply stained, sharply defined 

 nuclei. The chromatin of the nucleus is irregularly distributed, 

 forming numerous karyosomes, and the nuclear membrane is dis- 

 tinct. The cytoplasm is relatively devoid of granules, and unlike 

 that of the secreting epithelium does not possess a strong affinity 

 for the acid dyes (eosin, etc.). 



9. The Straight Collecting Tubules, These portions of the 

 tubules begin in the medullary rays, where they receive the arched 

 tubules, and, proceeding to the medulla, become considerably in- 

 creased in size. They penetrate the boundary zone of the medulla, 

 all pursuing a parallel or slightly convergent course, and occasion- 

 ally uniting with each other. On entering the papillary zone, by 



