1894.] 3IICR0SC0PICAL JOURNAL. 165 



The tubules are long and narrow tubes which do not run 

 straight but in a wavy course, and which are longer than 

 the diameter of the cortex. The ditFereut parts of the 

 tube are different in their cell structure. It is by the 

 difference of cell structure that we shall at first recog- 

 nize the various parts of the tubule; but the true way 

 is by tracing with infinite pains the connections between 

 all the different parts by the study of many sections and 

 many parts of sections. In fig. 3, a diagram of a tubule 

 is given. This shows that the tubules are not simple 

 but are branched, several uniting to form the terminal 

 tube. This end of the tube (a) lies in the malpighian 

 pyramid; it is called the "collecting tubule." It runs 

 out towards the cortex and finally branches into a num- 

 ber of portions from each of which a slender tube (d) 

 runs down and part way back. This is called the "loop 

 of Henle." 



The loop of Henle is followed by a thicker tubu- 

 lar portion (e), the " convoluted tubule," this runs into 

 the final part of the tube, the " malpighian corpuscle" 

 (e). This entire tube is one continuous organ made of 

 epithelium cells, one layer deep, with a central lumen 

 and surrounded with blood vessels ; it has thus the typ- 

 ical structure of a tubular gland. Let us attempt to 

 get a clear notion of the epithelium in each of the differ- 

 ent parts. In actually distinguishing these points on 

 sections it is necessary to remember that many of the 

 parts of tubule will be cut so as to present surface views, 

 and such will appear entirely different from sections pass- 

 ing through the centres of tubules. In the collecting 

 portion of the tubule the cells are cubical and clear and 

 are largely nucleated. The boundaries of the cells in this 

 region are more clearly seen. The cells do not, however, 

 have the columnar character which is seen in the cells 

 lining the ducts of such glands as the salivary glands 

 and the tubules of the stomach. The loops of Henle are 



