ORGANS OF THE BODY. 



523 



Each of these collecting tubes is accompanied by a number of smaller 

 passages. These, as we shall see presently, are the descending and 

 recurrent arms of the looped tubes of Henle, which are consequently 

 elements of the cortex both before and after traversing the boundary 

 layer. 



But what becomes of the collecting tubes on their arrival at the surface 

 of the kidney ? 



Fig. 517. Vertical section from the 

 kidney of the Guinea-pig (hydro- 

 chloric acid preparation), a, trunk 

 of a collecting tube; 6, branches 

 of the same; c, further subdivision; 

 d, convoluted canal (intercalated 

 portion); e, descending arm of a 

 loop tube; /, loop; g, recurrent 

 arm; and A, continuation as con- 

 voluted uriniferous tube of the 

 cortex. 



Fig. 518. The upper portion of a medul- 

 lary ray from the kidney of the pig; a 

 and d, so-called collecting tubes; 6, their 

 arched branches and continuation at c, 

 into the descending arms of the looped 

 canals. 



Maceration in acid (fig. 517) enables us to convince ourselves that on 

 their arrival here they give off numerous branches, and eventually break 

 up into arching, and, not unfrequently coiled tubules (d). The latter 

 may present in smaller animals a rugged appearance, not seen in larger 

 creatures. These are the " intercalated portions " of Sclmeigger-Seidel or 

 " connecting canals " of Roth. 



