308 



PRACTICAL HISTOLOGY. 



[XXVIIL 



capillaries (fig. 295). The basement membrane of the capsule is 

 continuous by a narrow neck with the basement membrane of a 

 convoluted tubule, but it is only in the rare case where the section 



cuts the capsule at this level that 

 this connection is seen. This con- 

 nection must usually be made out 

 on isolated tubules, although some- 

 times it is seen in sections of a 

 mouse's kidney. 



(e.) The convoluted tubules, 

 with a sinuous or twisted course, 

 cut some longitudinally and others 

 transversely. Each tube is lined 

 by a single layer of cells, the indi- 

 vidual cells not sharply mapped off 

 from each other, and leaving a 

 small lumen in the centre. The 

 outer part of each cell is striated 

 or " rodded," and near its centre 

 it contains a spheroidal nucleus 



FIG, 295. Glomenilus and Sections of Con- ic. a 9r> A\ 



voluted Tubules of a Kidney, x 300. ^ /, Vr , m , , 



(/..) Irregular Tubules. Here 



and there in the cortex may be seen zigzag portions of tubules 

 of unequal width, and usually more deeply stained than the rest, 



and the epithelium dis- 

 tinctly rodded (fig. 297). 

 (<).} Note the small 

 amount of connective 

 tissue between the tub- 

 ules of the cortex. It 

 is best seen just outside 

 the Malpighian capsules. 

 It is far more abundant 

 in the medulla, 



(h.) In the medulla, the straight tubes, which are largest and 

 widest where they are about to open on the apex of a Malpighian 



pyramid discharging tubules but 

 it is not so easy to get a section 

 showing this, as from their radial 

 arrangement they are apt to be cut 

 obliquely. The collecting and dis- 

 charging tubes have a wide lumen, 

 and are lined by a layer of clear 

 columnar cells with ovoid "tmdei. Trace the straight tubules out- 

 wards towards the surface ; they become smaller, still their lumen 



FlG 296. Rodded Epithelium of a Convoluted Tubule. 

 Ammonium ehromate. 



FlG. 207. Irregular Tubule, Kidney of 

 Dog. Muller'B fluid. 



