THE UKIXIFEKOUS TUBULES 343 



united by a very delicate but scanty connective tissue containing 

 no elastic fibres. 



The visceral layer of Bowman's capsule is firmly adherent to 

 the walls of the glomerular capillaries. It consists of a single 

 layer of flat epithelial cells which are intimately blended with each 

 other and with the endothelium of the capillaries. The epithelial 

 cells possess a clear cytoplasm and a flattened ovoid nucleus, which, 

 being thicker than the body of the cell, produces a considerable 

 bulging. In fetal and infantile life the shape of the cells of this 

 layer is cuboidal or even low columnar, but becomes more and 

 more flattened as development progresses, until the epithelium 

 finally simulates a layer of endothelial cells. 



The epithelium of the parietal layer of Bowman's capsule is 

 also cuboidal in fetal life, but during development becomes nearly 

 as much flattened as that of the visceral layer. Its single layer of 

 finely granular cells forms a complete lining for the capsule. It 

 rests upon a homogeneous basement membrane which is invested 

 by a thin layer of connective tissue. This fibrous layer is rather 

 more highly developed about those Malpighian bodies which lie 

 near the medulla than about those of the more peripheral por- 

 tions of the cortex. 



2. The Neck of the Tubule. In this portion of the tubule the 

 flattened epithelium of Bowman's capsule rapidly changes to the 

 low columnar type of the proximal convoluted portion. This 

 section is extremely short ; it forms a constricted portion which 

 marks the beginning of the tortuous tubule. This constriction is 

 more apparent than real, since the caliber of the tubule in the 

 neck is as great as in the succeeding portion whose external diam- 

 eter is, however, much increased by the increasing height of the 

 epithelial cells. This portion of the tubule, being in relation with 

 the Malpighian body, is necessarily found in the cortical labyrinth. 



3. The Proximal Convoluted Portion (Tubulus Contortus, First 

 Convoluted Tubule, Convoluted Tubule of the First Order). This 

 is the longest and broadest portion of the uriniferous tubule. Col- 

 lectively the convoluted tubules form the greater part of the cor- 

 tical labyrinth, in which region only they occur. This portion of 

 the tubule is remarkable for the irregularity of its course, it being 

 twisted and bent upon itself in a most tortuous manner. Arising 

 at the Malpighian body, it at first passes toward the surface of the 

 organ (Golgi*), but soon turns about and runs toward the medulla, 



*Rend. d. r. accad. d. Lincci, 1889. 



