492 



OF SECRETION AND EXCRETION. 



received the name of the Malpighiau Capsule. 1 The total number of the 

 tubes is estimated by Huschke at about two millions. The epithelium pre- 

 sents very considerable changes in its character in the different parts of the 

 tube. In the tortuous cortical part the cells are cloudy, and not very dis- 

 tinctly differentiated from one another, the nuclei lying in a pulpy sub- 

 stance, which is but loosely attached to the basement-membrane, slight 

 pressure causing it to exude from the divided tubules under the microscope. 

 These cells contain fat-drops and numerous dark granules that conceal the 



FIG. 179. 



FIG. ISO. 



FIG. 179. Diagram of the course of the Uriniferous Tubules : a, orifice of tubule at apex of Mal- 

 pighian pyramid; 6, intermediary portion, continuous with recurrent branches, which form loops, c, 

 in the medullary portion, of the kidney, and reascending, terminate in Malpighiau capsules in the 

 cortical portion. 



FIG. 180. Uriniferous Tube, Malpighian Tuft and Capsule, from Kidney of Frog : a, cavity of the 

 tube; 6, epithelium of the tube; &', ciliated epithelium of the neck of the capsule; b", detached epi- 

 thelium scale; c, basement-membrane of tube; c', basement-membrane of capsule; m, convoluted 

 capillaries of the Malpighian tuft. 



nucleus, but clear away with dilute acids. The capsular limb of the loop of 

 Henle is lined by a thin and clear continuous layer, which is raised at reg- 

 ular intervals by nuclei. In the wider part of the opposite limb of the loop 

 the pulp presents a fissure midway between each pair of adjoining nuclei ; 

 so that the epithelium appears in the form of well-defined columnar cells 



1 Ludwig states that the tubuli uriniferi change their diameter no less than seven 

 times, viz.: 1. At the constriction at the nock of the capsule; 2. At the dilatation 

 extending from the neck of the capsule through the tortuous portion ; 3. At the 

 constriction through the greater part of the loop of Henle; 4. At the dilatation in 

 the ascending limb of the loop; 5. At the constriction where it becomes continuous 

 with the windings of the intermediary portion ; G. At the dilatation in these latter; 

 and 7. At the constriction in the portion that extends from the intermediary portion 

 to the excretory ducts. 



