260 



STETJCTUEE OF GLANDS, 



of the kidneys in the vertebrate series is of especial interest. 



In fishes and amphibia the entire tissue of the kidney con- 

 sists of tortuous canals, which 

 end partly in blind extremi- 

 ties, and partly pass into one 

 another in loops, but which, 

 from their great length and 

 intimate connection, cannot be 

 demonstrated singly. They 

 are not divided into single py- 

 ramids or lobules, a peculiarity 

 that first makes its appearance 

 among birds. Here the highly 

 tortuous uriniferous tubules 

 furnished with lateral 



Fig. 261 Termination of one of 

 the tubuli uriniferi from the kidney 

 of an adult, examined soon after 

 death. The cellular structure is con- 

 spicuous. Magnified 250 times. 



are 



branches, which come off like 

 the tines of a stag's horn ; in 

 all probability they pass over 

 the one into the other by means 

 of loops. In the mammalia 

 the tubuli uriniferi form many 

 pyramids or lobes, each a 

 system by itself (figs. 258 and 

 259, A). In the cortical sub- 

 stance of the human kidney 

 the tubuli can be traced, al- 

 though with difficulty, wind- 

 ing among the vascular plex- 

 uses or skeins, mostly looped 

 towards the margin of the or- 

 gan, and running into one 

 another (fig. 260, b, b), or 



Fig. 262. A lohe of the kidney ending blindly (a), more 

 of the adult porpoise (Delpkinu, , H M enl ed and 



phoccena). After Muller. 111 & i /. 



club-shaped (fig. 261), occa- 

 sionally also cleft (fig. 260, c). The entire cortical substance 

 consists of convolutions of the uriniferous tubules, which are 

 found to present a very nearly uniform diameter, and which, 

 on an average, may be from about' the 50th to the 60th of a 

 line. They unite two and two as they approach the tubular 

 or medullary structure, becoming at the same time somewhat 



